Display device

ABSTRACT

To provide a high-performance and highly reliable display device with a high aperture ratio, including light-emitting elements, and a manufacturing method thereof, and a technique for manufacturing such a display device at a low cost with high productivity. A compensating circuit, a light-emitting element, a switch, and a transistor are included, in which one terminal of the switch is electrically connected to the compensating circuit, a gate of the transistor is electrically connected to the compensating circuit, one of a source and a drain of the transistor is electrically connected to a first electrode of the light-emitting element, the other of the source and the drain of the transistor is maintained at a certain potential, and a second electrode of the light-emitting element and the other terminal of the switch are electrically connected to the same wire.

BACKGROUND OF THE PRESENT INVENTION

1. Field of the Present Invention

The present invention relates to a display device using a light-emittingelement.

2. Description of the Related Art

In recent years, development of an electroluminescence (ElectroLuminescence) display device in which thin film transistors (hereafteralso referred to as “TFTs”) are integrated over a substrate hasprogressed. In such a display device, thin film transistors aremanufactured over a substrate by using thin-film formation technologyand a light-emitting element (electroluminescence (hereinafter alsoreferred to as “EL”) element) is formed as a display element overvarious circuits including the thin film transistors.

In pixels of a display device using light-emitting elements, respectiveamounts of current flowing into the light-emitting elements varydepending on variations of electrical characteristics such as eachthreshold voltage of TFTs for forming the pixels, so that there is aproblem of variation in luminance of the light-emitting elements. Astructure in which such variation in threshold voltage of TFTs iscompensated using a capacitor has been disclosed (e.g., see PatentDocument 1: U.S. Pat. No. 6,229,506).

SUMMARY OF THE PRESENT INVENTION

In the above-described pixel configuration, however, the aperture ratioof each pixel may be reduced since it is necessary to form a pluralityof wires within each pixel. Further, the wires are densely-disposed,thereby the wire structure becomes complex and dense. Therefore, whenthe process becomes difficult and complex, the number of defects mightbe increased, and a yield is decreased.

In view of the foregoing, it is an object of the present invention toprovide a high-performance and highly reliable display device with ahigh aperture ratio, including light-emitting elements, and amanufacturing method thereof. In addition, it is another object of thepresent invention to provide a technique for manufacturing a displaydevice at a low cost with high productivity.

The present invention can be used for a display device having a displayfunction. The display device using the present invention includes, e.g.,a display device in which a light-emitting element where a layercontaining either an organic substance which exhibits light emissioncalled electroluminescence (hereinafter also referred to as “EL”) or acombination of organic and inorganic substances is interposed betweenelectrodes is connected to a TFT.

Note that a “semiconductor device” in this specification means a devicecapable of functioning by utilizing semiconductor characteristics.Therefore, a display device including a transistor or the like can alsobe assumed as a semiconductor device.

In one feature of the display device of the present invention, acompensating circuit, a light-emitting element, a switch, and atransistor are included, in which one terminal of the switch iselectrically connected to the compensating circuit, a gate of thetransistor is electrically connected to the compensating circuit, one ofa source and a drain of the transistor is electrically connected to afirst electrode of the light-emitting element, the other of the sourceand the drain of the transistor is maintained at a fixed potential, anda second electrode of the light-emitting element and the other terminalof the switch are electrically connected to the same wire.

In one feature of the display device of the present invention, acompensating circuit, a light-emitting element, a first switch, a secondswitch, a transistor, and a controlling circuit are included, in whichone terminal of the controlling circuit is maintained at a fixedpotential, one terminal of the first switch is electrically connected tothe compensating circuit, one terminal of the second switch iselectrically connected to the compensating circuit, the other terminalof the second switch is electrically connected to a first wire, a gateof the transistor is electrically connected to the compensating circuit,one of a source and a drain of the transistor is electrically connectedto a first electrode of the light-emitting element, the other of thesource and the drain of the transistor is electrically connected to theother terminal of the controlling circuit, and a second electrode of thelight-emitting element and the other terminal of the first switch areelectrically connected to the same second wire.

In one feature of the display device of the present invention, alight-emitting element, a first switch, a second switch, a transistor, afirst capacitor, and a second capacitor are included, in which oneterminal of the first switch is electrically connected to a firstelectrode of the second capacitor, a second electrode of the secondcapacitor is electrically connected to one terminal of the second switchand one electrode of the first capacitor, a second electrode of thefirst capacitor is maintained at a fixed potential, a gate of thetransistor is electrically connected to the first electrode of thesecond capacitor, one of a source and a drain of the transistor iselectrically connected to a first electrode of the light-emittingelement, the other of the source and the drain of the transistor iselectrically connected to the other terminal of the second switch and ismaintained at a fixed potential, and a second electrode of thelight-emitting element and the other terminal of the first switch areelectrically connected to the same wire.

In one feature of the display device of the present invention, alight-emitting element, a first switch, a second switch, a third switch,a fourth switch, a transistor, a first capacitor, and a second capacitorare included, in which one terminal of the fourth switch is maintainedat a fixed potential, one terminal of the first switch is electricallyconnected to a first electrode of the second capacitor, a secondelectrode of the second capacitor is electrically connected to oneterminal of the second switch and a first electrode of the firstcapacitor, a second electrode of the first capacitor is maintained at afixed potential, one terminal of the third switch is electricallyconnected to the second electrode of the second capacitor, the otherterminal of the third switch is electrically connected to a first wire,a gate of the transistor is electrically connected to the firstelectrode of the second capacitor, one of a source and a drain of thetransistor is electrically connected to a first electrode of thelight-emitting element, the other of the source and the drain of thetransistor is electrically connected to the other terminal of the secondswitch and the other terminal of the fourth switch, and a secondelectrode of the light-emitting element and the other terminal of thefirst switch are electrically connected to the same second wire.

By using the present invention, since the number of wires can be reducedin each pixel, the aperture ratio can be improved and the manufacturingprocess can be simplified. Consequently, such a highly reliable displaydevice can be manufactured with a high yield. In addition, the presentinvention can manufacture a display device at a low cost with goodproductivity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are schematic diagrams showing the present invention.

FIGS. 2A and 2B are circuit diagrams for showing a pixel configurationapplicable to a display device of the present invention.

FIGS. 3A and 3B are cross-sectional views for showing a display deviceof the present invention.

FIGS. 4A and 4B are circuit diagrams for showing a pixel configurationapplicable to a display device of the present invention.

FIGS. 5A and 5B are circuit diagrams for showing a pixel configurationapplicable to a display device of the present invention.

FIGS. 6A and 6B are circuit diagrams for showing a pixel configurationapplicable to a display device of the present invention.

FIGS. 7A and 7B are circuit diagrams for showing a pixel configurationapplicable to a display device of the present invention.

FIGS. 8A and 8B are circuit diagrams for showing a pixel configurationapplicable to a display device of the present invention.

FIGS. 9A and 9B are circuit diagrams for showing a pixel configurationapplicable to a display device of the present invention.

FIGS. 10A and 10B are circuit diagrams for showing a pixel configurationapplicable to a display device of the present invention.

FIGS. 11A and 11B are circuit diagrams for showing a pixel configurationapplicable to a display device of the present invention.

FIGS. 12A and 12B are cross-sectional views for showing a display deviceof the present invention.

FIGS. 13A and 13B are views for showing a display device of the presentinvention.

FIGS. 14A and 14B are cross-sectional views for showing a display deviceof the present invention.

FIGS. 15A to 15D are diagrams for showing a structure of alight-emitting element applicable to the present invention.

FIGS. 16A to 16C are cross-sectional views for showing a display deviceof the present invention.

FIGS. 17A to 17C are top views each of a display device of the presentinvention.

FIGS. 18A and 18B are top views each of a display device of the presentinvention.

FIGS. 19A to 19E are diagrams for showing a protection circuit to whichthe present invention is applied.

FIG. 20 is a block diagram showing a main structure of an electronicdevice to which the present invention is applied.

FIGS. 21A and 21B are diagrams for showing an electronic device to whichthe present invention is applied.

FIG. 22 is a diagram showing an electronic device to which the presentinvention is applied.

FIG. 23 is a cross-sectional view showing a display device of thepresent invention.

FIGS. 24A to 24E are diagrams for showing an electronic device to whichthe present invention is applied.

FIGS. 25A and 25B are circuit diagrams for showing a pixel configurationapplicable to a display device of the present invention.

FIGS. 26A and 26B are schematic diagrams showing the present invention.

FIGS. 27A and 27B are schematic diagrams showing the present invention.

FIGS. 28A and 28B are schematic diagrams showing the present invention.

FIGS. 29A and 29B are cross-sectional views for showing a display deviceof the present invention.

FIGS. 30A and 30B are top views for showing a display device of thepresent invention.

FIGS. 31A and 31B are top views for showing a display device of thepresent invention.

FIGS. 32A and 32B are top views for showing a display device of thepresent invention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

Although the present invention will be fully described by way ofembodiment modes with reference to the accompanying drawings, it is tobe understood that various changes and modifications will be apparent tothose skilled in the art. Therefore, unless such changes andmodifications depart from the scope of the present invention, theyshould be construed as being included therein. Note that the sameportions or the portions having the same functions are denoted by theidentical reference numerals in the drawings, and description thereof isomitted.

Embodiment Mode 1

An embodiment mode of the present invention will be described usingFIGS. 1A and 1B. A pixel shown in FIG. 1A includes a transistor 101,switches 102 and 103, a light-emitting element 104, controlling circuits105 a and 105 b, and a compensating circuit 106. The present inventionis not limited to the configuration of FIGS. 1A and 1B; all of theabove-described components are not necessarily included.

FIG. 1B shows an example in which transistors 152 and 153 are used asthe switches 102 and 103 respectively in FIG. 1A. The transistor 101 isa transistor for controlling light-emission of the light-emittingelement, the transistor 153 is a transistor for controlling a videosignal input to the pixel, a wire 107 is a wire for sending the videosignal, a wire 108 is a wire maintained at a certain potential, and awire 109 is a wire maintained at a certain potential. Respectivepotentials of the wires 108 and 109 are different, and have a potentialdifference.

Each conductivity type of the transistors 101, 152, and 153 may beeither n-channel or a p-channel.

A gate of the transistor 153 is connected to a wire 110, one of a sourceand a drain thereof is connected to the wire 107, and the other of thesource and the drain thereof is connected to the compensating circuit106. A gate of the transistor 152 is connected to a fifth wire 111, oneof a source and a drain thereof is connected to the compensating circuit106, and the other of the source and the drain thereof is connected tothe wire 109.

A gate of the transistor 101 is connected to the compensating circuit106, one of a source and a drain thereof is connected to the controllingcircuit 105 a, and the other of the source and the drain thereof isconnected to the controlling circuit 105 b. The controlling circuit 105b is connected to a first electrode of the light-emitting element 104.The controlling circuit 105 a is connected to the wire 108, and a secondelectrode of the light-emitting element 104 is connected to the wire109. According to the present invention, the transistor 152 and thelight-emitting element 104 are connected to the common wire 109 in FIG.1B.

Further, as shown in FIG. 26A, one terminal of the switch 102 may beconnected not to the compensating circuit 106 but to the controllingcircuit 105 b, and the other terminal thereof may be connected to thewire 109. As shown in FIG. 26B, one of a source and a drain of thetransistor 152 may be connected not to the compensating circuit 106 butto the controlling circuit 105 b, and the other of the source and thedrain thereof may be connected to the wire 109.

Further, as shown in FIG. 27A, one terminal of the switch 102 may beconnected not to the compensating circuit 106 but to the controllingcircuit 105 a, and the other terminal thereof may be connected to thewire 109. As shown in FIG. 27B, one of a source and a drain of thetransistor 152 may be connected not to the compensating circuit 106 butto the controlling circuit 105 a, and the other of the source and thedrain thereof may be connected to the wire 109.

Further, as shown in FIGS. 28A and 28B, no controlling circuit 105 a maybe included, the compensating circuit 106 may be connected to the wire108, and one of a source and a drain of the transistor 101 may beconnected to the compensating circuit 106. As described above, theposition of the switch 102 (the transistor 152) in the pixel of thepresent invention is not limited to that shown in FIGS. 1A and 1B; theswitch 102 (the transistor 152) may also be arbitrarily as shown inFIGS. 26A to 28B. As described above, the pixel of the present inventionmay also have a configuration including not both of the controllingcircuits 105 a and 105 b but only one of the controlling circuits 105 aand 105 b.

FIGS. 2A and 2B each show an example of a pixel to which the presentinvention is applied, in which the compensating circuit 106 and thecontrolling circuits 105 a and 105 b in FIGS. 1A and 1B are morespecifically described. The pixel shown in FIG. 2A includes thetransistor 101, the switches 102 and 103, a light-emitting element 104,switches 121 and 122, and capacitors 123 and 124. In the pixel shown inFIG. 2A, the switch 122 and the capacitors 123 and 124 correspond to thecompensating circuit 106 in FIG. 1A, and the switch 121 corresponds tothe controlling circuit 105 a in FIG. 1A. In the pixel shown in FIG. 2B,a transistor 162 and the capacitors 123 and 124 correspond to thecompensating circuit 106 in FIG. 1B, and a transistor 161 corresponds tothe controlling circuit 105 a in FIG. 1B.

FIG. 2B shows an example in which transistors 152 and 153 and thetransistors 161 and 162 are used as the switches 102, 103, 121, and 122in FIG. 2A.

A gate of the transistor 153 is connected to the wire 110, one of asource and a drain thereof is connected to the wire 107, and the otherof the source and the drain thereof is connected to a first electrode ofthe capacitor 124 and one of a source and a drain of the transistor 162.A gate of the transistor 162 is connected to a wire 130, one of a sourceand a drain thereof is connected to a first electrode of the capacitor123, and the other of the source and the drain thereof is connected toone of a source and a drain of the transistor 161 and one of a sourceand a drain of the transistor 101. A gate of the transistor 161 isconnected to a wire 131, and the other of the source and the drainthereof is connected to the wire 108.

A second electrode of the capacitor 123 is connected to the wire 108. Asecond electrode of the capacitor 124 is connected to one of a sourceand a drain of the transistor 152 and a gate of the transistor 101. Agate of the transistor 152 is connected to the wire 111, and the otherof the source and the drain thereof is connected to the wire 109. Theother of the source and the drain of the transistor 101 is connected toa first electrode of the light-emitting element 104. A second electrodeof the light-emitting element 104 is connected to the wire 109.According to the present invention, the transistor 152 and thelight-emitting element 104 are connected to the common wire 109 in FIG.2B.

First, the switches 121, 122, and 102 are turned ON and the switch 103is turned OFF. Thereby a current flows from the wire 108 to the wire 109through the switches 121 and 122, the second capacitor 124, and theswitch 102, so that electric charge is charged in the second capacitor124. When the voltage held in the second capacitor 124 exceeds thethreshold voltage of the transistor 101, the transistor 101 is turnedON. When the transistor 101 is turned ON, a current flows from the wire108 to the wire 109 through the switch 121, the transistor 101, and thelight-emitting element 104.

Next, the switches 122 and 102 are turned ON, and the switches 121 and103 are turned OFF. The electric charge held in the second capacitor 124is discharged, so that a current flows through the switch 122, thetransistor 101, the light-emitting element 104, the switch 102 and thesecond capacitor 124. When a voltage value between both the electrodesof the second capacitor 124, which is namely a voltage value between thegate and the source of the transistor 101, becomes equal to thethreshold voltage of the transistor 101, the transistor 101 is turnedOFF, so that the discharge of the electric charge held in the secondcapacitor 124 is completed.

Next, the switches 121, 122, 102, and 103 are turned OFF. Thereby thethreshold voltage of the transistor 101 is held in the second capacitor124.

Subsequently, the switch 103 is turned ON, and the switches 102, 121,and 122 are turned OFF. Thereby a video signal is outputted to the wire107, so that the wire 107 has a potential VD of the video signal. Sincethe threshold voltage of the transistor 101 is held in the secondcapacitor 124, the gate potential of the transistor 101 becomes apotential (VD+Vth) obtained by adding the threshold voltage (Vth) of thetransistor 101 to the video signal potential VD inputted from the wire107. Thereby the transistor 101 is turned ON.

When the writing of the video signal is completed, the switch 103 isturned OFF. After that, the video signal output to the wire 107 iscompleted, so that a certain potential is maintained.

Then, the switch 121 is turned ON. Since the transistor 101 has beenalready turned ON, a current flows from the wire 108 to thelight-emitting element 104 through the switch 121 and the transistor101. Thereby the light-emitting element 104 emits light. At this time,the current value flowing into the light-emitting element 104 depends onthe voltage value between the gate and the source of the transistor 101.When the potential of the wire 108 is Va, the voltage value between thegate and the source of the transistor 101 at this time is (Va−(VD+Vth)).Here, even if the threshold voltage (Vth) of the transistor 101 variesbetween the pixels, a voltage depending on the variation is held in thesecond capacitor 124 in each pixel. Accordingly, the luminance of thelight-emitting element 104 is not affected by the variation in thresholdvoltage of the transistor 101.

The luminance of the light-emitting element which is a load has aproportional relation to the current which flows into the light-emittingelement. Therefore, the present invention in which the amount of currentto be supplied to the light-emitting element is controlled can controlthe luminance of the light-emitting element easier than the case wherethe amount of voltage to be supplied to the light-emitting element iscontrolled.

In addition, the present invention in which the amount of current to besupplied to the light-emitting element is controlled can flow apredetermined current to the light-emitting element even if thevoltage-current characteristics of the light-emitting element is changedby deterioration, temperature change, or the like of the light-emittingelement. Accordingly, variation in luminance of the light-emittingelement can be suppressed.

Further, a configuration in which a switch is provided in addition toeach pixel configuration shown in FIGS. 2A and 2B may also be employed.A configuration in which a switch 125 is provided is shown in each ofFIGS. 25A and 25B. In FIG. 25A, one terminal of the switch 125 isconnected to one terminal of the switch 102, and the other terminalthereof is connected to a first electrode of the light-emitting element104. FIG. 25B shows an example in which a transistor 165 is used as theswitch 125. In FIG. 25B, a gate of the transistor 165 is connected to awire 133, one of a source and a drain thereof is connected to one of asource and a drain of the transistor 152, which is connected to the wire109, and the other of the source and the drain of the transistor 165 isconnected to a first terminal of the light-emitting element 104.

In the present invention, the second electrode of the light-emittingelement 104 and the switch 102 (the transistor 152) are connected to thecommon wire 109. Cross-sectional views of the pixels are FIGS. 3A and3B. FIGS. 3A and 3B correspond to the pixels shown in FIGS. 2A and 2B,in which the transistors 101 and 152 are formed over a substrate 200with an insulating layer 201 which functions as a base layer interposedtherebetween. Although an example in which top-gate thin filmtransistors are used as the transistors 101 and 152 is described in thisembodiment mode, the present invention is not limited to thisconfiguration; a bottom-gate thin film transistor may also be used.

In FIG. 3A, the transistor 101 includes a semiconductor layer 210, agate insulating layer 202, a gate 211, a wire 212 a, and a wire 212 b,and the transistor 152 includes a semiconductor layer 220, the gateinsulating layer 202, a gate 221, a wire 222 a, and a wire 222 b. Overthe transistors 101 and 152, an insulating layer 203 which functions asan interlayer insulating layer and an insulating layer 204 whichfunctions as a partition wall of a light-emitting element are formed.

A first electrode 230 is formed in contact with the wire 222 b, so thatthe transistor 101 and the light-emitting element 104 are electricallyconnected to each other. The light-emitting element 104 is structured bystacking the first electrode 230, an electroluminescence layer 231, anda second electrode 232. The wire 109 is formed over the insulating layer203 by the same step as the first electrode 230 so as to be in contactwith the wire 222 b of the transistor 152, so that the transistor 152and the wire 109 are electrically connected to each other. Further, thesecond electrode 232 of the light-emitting element 104 is in contactwith the wire 109 at an opening (also called “contact hole) formed inthe insulating layer 204 so as to reach the wire 109, so that thelight-emitting element 104 and the wire 109 are electrically connectedto each other.

FIG. 3B shows an example in which the stack structure of the wire 212 bof the transistor 101 and the first electrode 230 of the light-emittingelement 104 and the stack structure of the wire 222 b of the transistor152 and the wire 109 are different from those in FIG. 3A. In the processof FIG. 3A, the wires 212 b and 222 b are formed, and then the firstelectrode 230 and the wire 109 are formed. On the other hand, in theprocess of FIG. 3B, the first electrode 230 and the wire 109 are formedover the insulating layer 203 in advance, and then the wires 212 b and222 b are formed. Thus, the stack order of FIG. 3A is opposite to thatof 3B. The following advantages exist respectively in FIGS. 3A and 3B:contamination of an etching residue or the like on a surface of thefirst electrode 230 can be prevented in FIG. 3A; coverage is good sincethe first electrode 230 is formed in a flat region and the wire 212 b isstacked, grinding treatment such as CMP can be sufficiently performed sothat formation with high flatness can be performed in FIG. 3B.

FIGS. 14A and 14B each show an example in which the wire 109 is formedby the same step as gates of the transistors 152 and 101 in the displaydevices of FIGS. 3A and 3B. In FIGS. 4A and 14B, the wire 109 is formedover the gate insulating layer 202. In FIG. 14A, the wire 222 b of thetransistor 152 is electrically connected by forming so as to be incontact with the wire 109 at an opening formed in the insulating layer203, and the second electrode 232 of the light-emitting element 104 iselectrically connected to the wire 109 via the wire 222 b. In FIG. 14B,the second electrode 232 of the light-emitting element 104 is directlyto the wire 109 at an opening formed in the insulating layers 203 and204, so that the wire 222 b and the second electrode 232 areelectrically connected to each other via the wire 109.

Further, FIG. 23 shows an example in which the wire 109 is manufacturedby the same step as the wire 222 b. In FIG. 23, the wire 109 and thewire 222 b are manufactured by the same step and the wire 109 and thewire 222 b are the same common wire. The second electrode 232 of thelight-emitting element 104 is formed so as to be in contact with thiswire which functions as both the wire 109 and the wire 222 b, so thatthe wires 109 and 222 b and the second electrode 232 are electricallyconnected to each other.

FIGS. 29A and 29B each show an example in which an insulating layer 206is formed as an interlayer insulating layer over the insulating layer203. In FIG. 29A, the insulating layer 206 is formed over thetransistors 152 and 101 and the insulating layer 203, and the wire 109and the first electrode 230 are formed at openings formed in theinsulating layer 206. The wire 212 b of the transistor 101, which isformed so as to be in contact with the first electrode 230 at theopening formed in the insulating layer 206, is electrically connected tothe first electrode 230. The wire 222 b of the transistor 152, which isformed so as to be in contact with the wire 109 at the opening formed inthe insulating layer 206, is electrically connected to the wire 109. Thesecond electrode 232 of the light-emitting element 104, which is formedso as to be in contact with the wire 109 at an opening formed in theinsulating layer 204, is electrically connected to the wire 109.

FIG. 29B shows an example in which the connection region between thesecond electrode 232 and the wire 109 is larger than that in FIG. 29A.As described above, any connection mode may be applied to connectionbetween the second electrode 232 and the wire 109; in addition, althoughthe number of connection points is one in FIGS. 29A and 29B, they may beconnected at plural points and the shape for connection can be setarbitrarily. As described above, as long as the transistor 152 and thelight-emitting element 104 are electrically connected to the same wire109, the wire 109 may be manufactured at any step in manufacturing thedisplay device, and layout can be set arbitrarily.

In the case where a plurality of insulating layers are connected by aplurality of wires through openings (contact holes) as shown in FIG.29A, respective openings formed in the insulating layers may be eitheroverlapped or not overlapped. For example, in the example of FIG. 29A,the opening for forming the wire 222 b of the insulating layer 203, theopening for forming the wire 109 of the insulating layer 206, and theopening for forming the second electrode 232 of the insulating layer 204are not overlapped one another. Further, a continuous opening may beformed in the insulating layers 203, 206, and 204 as well.

FIGS. 12A and 12B each show an example in which an inverted staggered,channel-etch type thin film transistor is used as a transistor.

In FIG. 12A, a transistor 141 includes a semiconductor layer 250, a gateinsulating layer 242, a semiconductor layer 253 a having oneconductivity type, a semiconductor layer 253 b having one conductivitytype, a gate 251, a wire 252 a, and a wire 252 b, and a transistor 142includes a semiconductor layer 260, a semiconductor layer 263 a havingone conductivity type, a semiconductor layer 263 b having oneconductivity type, the gate insulating layer 242, a gate 261, a wire 262a, and a wire 262 b. Over the transistors 141 and 142, an insulatinglayer 245 which functions as an interlayer insulating layer and aninsulating layer 244 which functions as a partition wall of alight-emitting element are formed. In this embodiment mode, theinsulating layer 245 is an inorganic film formed using an inorganicmaterial.

The first electrode 230 is formed so as to be in contact with the wire252 b at an opening formed in the insulating layer 245, so that thetransistor 141 and the light-emitting element 104 are electricallyconnected to each other. The light-emitting element 104 is structured bystacking the first electrode 230, the electroluminescence layer 231, andthe second electrode 232. The wire 109 is formed by the same step as thefirst electrode 230 so as to be in contact with the wire 262 b of thetransistor 142 at an opening formed in the insulating layer 245, so thatthe transistor 142 and the wire 109 are electrically connected to eachother. Further, the second electrode 232 of the light-emitting element104 is in contact with the wire 109 at an opening (also called “contacthole”) formed in the insulating layer 244 so as to reach the wire 109,so that the light-emitting element 104 and the wire 109 are electricallyconnected to each other.

FIG. 12A shows an example in which an amorphous semiconductor layerformed of amorphous silicon is used as each of the semiconductor layers250 and 260, and a semiconductor film imparting n-type conductivity isused as each of the semiconductor layers 253 a, 253 b, 263 a, and 263 bhaving one conductivity type. The semiconductor layers 253 a, 253 b, 263a, and 263 b having one conductivity type are not necessarily provided;they may be arbitrarily provided.

FIG. 12B shows an example in which an insulating layer 246 which isparticularly advantageous as a flattening film is formed over theinsulating layer 245. In FIG. 12B, the insulating layer 246 ispreferably formed of an organic material in order to flatten convex andconcave formed by the transistors 142 and 141.

In FIG. 12B, the first electrode 230 is formed so as to be in contactwith the wire 252 b at an opening formed in the insulating layers 245and 246, so that the transistor 141 and the light-emitting element 104are electrically connected to each other. The wire 109 is formed by thesame step as the first electrode 230 so as to be in contact with thewire 262 b of the transistor 142 at an opening formed in the insulatinglayers 245 and 246, so that the transistor 142 and the wire 109 areelectrically connected to each other. Further, the second electrode 232of the light-emitting element 104 is in contact with the wire 109 at anopening (also called “contact hole”) formed in the insulating layer 244so as to reach the wire 109, so that the light-emitting element 104 andthe wire 109 are electrically connected to each other.

As described above, the transistor of the present invention is notparticularly limited; either a top-gate transistor or a bottom-gatetransistor may be arbitrarily used. In addition, either a planertransistor or a staggered transistor may be used.

The second electrode layer of the light-emitting element and thetransistor in each pixel are electrically connected to each other viathe common wire. Connection examples between the second electrode andthe wire will be described using FIGS. 30A to 32B.

In FIG. 30A, first electrodes 501 a to 501 i of light-emitting elementsfor forming pixels are disposed contiguously in vertical and horizontaldirections, and insulating layers 503 a to 503 c each of which functionsas a partition wall are formed around the pixels. In FIG. 30A, anopening of the insulating layer is formed between the first electrodes501 a to 501 c and the first electrodes 501 d to 501 f so that a wire502 a is exposed. Similarly, an opening of the insulating layer isformed between the first electrodes 501 d to 501 f and the firstelectrodes 501 g to 501 i so that a wire 502 b is exposed. The wires 502a and 502 b which are formed at the openings of the insulating layerwhich are opened so as to divide the pixels in the horizontal directionof this figure, and a second electrode which is formed over the firstelectrodes 501 a to 501 i with an electroluminescence layer interposedtherebetween are formed so as to be in contact with each other to beelectrically connected to each other. In FIG. 30A, three pixelsincluding the first electrodes 501 d, 501 e, and 501 f respectively haveshape like a square, and a structure in which red (R), green (G), andblue (B) displays are performed by the first electrodes 501 d, 501 e,and 501 f, respectively may be employed. Note that pixel forms in FIGS.30B, and 31A to 32B are examples of the pixel form to which the presentinvention can be applied; the present invention is not limited to thisembodiment mode.

In FIG. 30B, first electrodes 511 a to 511 i of light-emitting elementsfor forming pixels are disposed contiguously in vertical and horizontaldirections, and insulating layers 513 a to 513 c each of which functionsas a partition wall are formed around the first electrodes of thepixels. In FIG. 30B, an opening of the insulating layer is formedbetween the first electrodes 511 a, 511 d, and 511 g and the firstelectrodes 511 b, 511 e, and 511 h so that a wire 512 a is exposed.Similarly, an opening of the insulating layer is formed between thefirst electrodes 511 b, 511 e, and 511 h and the first electrodes 511 c,511 f, and 511 i so that a wire 512 b is exposed. The wires 512 a and512 b which are formed at the openings of the insulating layer which areopened so as to divide the pixels in the vertical direction of thisfigure, and a second electrode which is formed over the first electrodes511 a to 511 i with an electroluminescence layer interposed therebetweenare formed so as to be in contact with each other to be electricallyconnected to each other.

In FIG. 31A, first electrodes 521 a to 521 i of light-emitting elementsfor forming pixels are disposed contiguously in vertical and horizontaldirections, and an insulating layer 523 which functions as a partitionwall is formed around the first electrodes of the pixels. An opening ofthe insulating layer 523 is formed between the first electrodes 521 cand 521 f so that a wire 522 a is exposed. Similarly, an opening of theinsulating layer 523 is formed between the first electrodes 521 f and521 i so that a wire 522 b is exposed. The wires 522 a and 522 b, and asecond electrode which is formed over the first electrodes 521 a to 521i with an electroluminescence layer interposed therebetween are formedso as to be in contact with each other to be electrically connected toeach other.

In FIG. 31A, unlike FIG. 30A or 30B where the opening to the wire isformed continuously for the pixels arranged in parallel, a connectionregion to the wire is provided by, in one pixel per plural pixels,reducing the area of the one pixel. In FIG. 31A, in the first electrodes521 d and 521 e which are pixels not provided with the connectionregions to the wire, the aperture ratio can be improved since an openingportion of the insulating layer 523 can be widely provided and the pixelregion can be widened. Furthermore, in the case where the display colorsof the pixels are red (R), green (G), and blue (B) (or may also be red(R), green (G), blue (B), and white (W)), the pixel size can be set asappropriate depending on the luminance or lifetime of each display colorof the pixels, thereby well-balanced precise display can be performed.

In FIG. 31B, first electrodes 531 a to 531 i of light-emitting elementsfor forming pixels are disposed contiguously in vertical and horizontaldirections, and an insulating layer 533 which functions as a partitionwall is formed around the first electrodes of the pixels. Openings ofthe insulating layer 523 are formed in forming portions of the firstelectrodes 531 a and 531 f respectively so that wires 532 a to 532 f areexposed. The wires 532 a to 532 f, and a second electrode which isformed over the first electrodes 531 a to 531 i with anelectroluminescence layer interposed therebetween are formed so as to bein contact with each other to be electrically connected to each other.In this manner, a structure in which the connection region to the wireis provided per first electrode for forming the pixel may also beemployed.

In FIG. 32A, first electrodes 541 a to 541 c of light-emitting elementsfor forming pixels are disposed contiguously in vertical and horizontaldirections, and insulating layers 543 a to 542 c each of which functionsas a partition wall are formed around the first electrodes of thepixels. The first electrodes of the pixels are arranged longitudinallyin plural number, and are adjacent to pixel regions 545 c, 546 c, 544 a,545 a, 546 a, 544 b, and 545 b, respectively. An opening of theinsulating layer is formed between the pixel regions 545 c and 546 c sothat a wire 542 a is exposed. Similarly, an opening of the insulatinglayer is formed between the pixel regions 546 a and 544 b so that a wire542 b is exposed. The wires 542 a and 542 b, and a second electrodewhich is formed over the first electrodes in the pixel regions with anelectroluminescence layer interposed therebetween are formed so as to bein contact with each other to be electrically connected to each other.

In the structure of FIG. 32A, unlike FIG. 30A where the wire is formedso as to divide the pixels per column, the connection region between thesecond electrode and the wire is provided per plural pixel regionshaving plural pixels. FIG. 32A shows a structure of a display device forperforming RGB color display; display is performed in the pixel regions544 a, 545 a, and 546 a with display colors of R, G, and B,respectively. Therefore, the opening of the insulating layer is providedper three colors of RGB in this example. Of course, the opening of theinsulating layer may be provided per four colors of RGBW in the casewhere display is performed with RGBW.

FIG. 32B shows an example in which an opening is provided in theinsulating layer which is a partition wall also in the horizontaldirection to form a connection region between the second electrode andthe wire. An insulating layer 553 a is formed so as to surround firstelectrodes 551 a to 551 c of light-emitting elements of pixels, and soas to surround the insulating layer 553 a, an opening of the insulatinglayer is formed to expose a wire 552. Similarly, an insulating layer 553b is formed so as to surround first electrodes 554 a to 554 c oflight-emitting elements of pixels, and so as to surround the insulatinglayer 553 b, an opening of the insulating layer is formed to expose thewire 552. The wire 552 which is formed so as to divide pixels per threepixels (which is in the case of RGB, or per four pixels in the case ofRGBW) in a reticular pattern, and a second electrode which is formedover the first electrodes in the pixel regions with anelectroluminescence layer interposed therebetween are formed so as to bein contact with each other to be electrically connected to each other.As described above, the connection between the second electrode and thewire can be performed with an arbitral structure, and the pixelstructure is not limited to this embodiment mode. Alignment of thepixels may be any one of the following arrangements: a stripearrangement in which pixels corresponding to red, green, and blue arearranged in stripes; a delta arrangement in which the pixels are shiftedby a half pitch per one line; and a mosaic arrangement in whichsub-pixels corresponding to red, green, and blue are arranged obliquely.The stripe arrangement which is suitable for displaying a line, afigure, text, and the like is preferably applied to a monitor. Themosaic arrangement which can provide a more natural image than thestripe arrangement is preferably applied to a television device and thelike. In addition, the delta arrangement which can also provide anatural image display is preferably applied to a television device andthe like.

If the number of wires which shut out light emitted from thelight-emitting element within the pixel is large, aperture ratio of thepixel is reduced in a bottom emission or dual emission display device.In the present invention, since the light-emitting element 104 and theswitch 102 (transistor 152) are connected in common to the same wireinstead of being connected to different wires each maintaining at acertain potential, a wire is not necessarily provided in plural numberwithin a pixel. Therefore, the number of wires within the pixel isreduced and the aperture ratio of the pixel can be improved.

Further, since dense disposition of wires can be prevented and the wirestructure does not become complex and dense in this structure, theprocess does not become complex. Therefore, shape defects by a complexprocess, pattern shape, or the like can be prevented, and a yield isimproved. Accordingly, a highly reliable display device can bemanufactured at a low cost with high productivity.

Embodiment Mode 2

A pixel configuration which is different from the above embodiment modewill be described using FIG. 4A.

A pixel includes transistors 8010 to 8015, capacitors 8016 and 8017, anda light-emitting element 8000. According to this pixel, one of a sourceand a drain of the transistor 8010 and one of a first electrode and asecond electrode of the light-emitting element 8000 are connected to thesame wire 8009.

In the pixel shown in FIG. 4A, the transistor 8012 and the capacitors8016 and 8017 correspond to the compensating circuit 106 in FIG. 1B, andthe transistors 8013 and 8015 correspond to the controlling circuit 105a in FIG. 1B.

ON/OFF of the transistors 8010 to 8013 and 8015 are controlled bysignals inputted though wires 8003 to 8006. Light emission/non-lightemission of the light-emitting element 8000 is controlled by a videosignal inputted though a wire 8001. Further, a power source is suppliedfrom a wire 8002 maintained at a certain potential to the above pixel.Note that the transistors included in the above pixel may be eithern-channel transistors or p-channel transistors.

Embodiment Mode 3

A pixel configuration which is different from the above embodiment modewill be described using FIG. 4B.

A pixel includes transistors 8110 to 8115, a capacitor 8116, and alight-emitting element 8100. The pixel may further include a capacitor8117. According to this pixel, one of a source and a drain of thetransistor 8110 and one of a first electrode and a second electrode ofthe light-emitting element 8100 are connected to the same wire 8109.

In the pixel shown in FIG. 4B, the transistors 8112 and 8113 and thecapacitors 8116 and 8117 correspond to the compensating circuit 106 inFIG. 1B, and the transistor 8115 corresponds to the controlling circuit105 b in FIG. 1B.

ON/OFF of the transistors 8110 to 8113 and 8115 are controlled bysignals inputted though wires 8103 to 8106. Light emission/non-lightemission of the light-emitting element 8100 is controlled by a videosignal inputted though a wire 8101. Further, a power source is suppliedfrom a wire 8102 maintained at a certain potential to the above pixel.Note that the transistors included in the above pixel may be eithern-channel transistors or p-channel transistors.

Embodiment Mode 4

A pixel configuration which is different from the above embodiment modewill be described using FIG. 5A.

A pixel includes transistors 8060 to 8064, a capacitor 8065, and alight-emitting element 8050. The pixel may further include a capacitor8066. According to this pixel, one of a source and a drain of thetransistor 8060 and one of a first electrode and a second electrode ofthe light-emitting element 8050 are connected to the same wire 8059.

In the pixel shown in FIG. 5A, the transistor 8062 and the capacitors8050 and 8066 correspond to the compensating circuit 106 in FIG. 1B, andthe transistor 8064 corresponds to the controlling circuit 105 b in FIG.1B.

ON/OFF of the transistors 8060 to 8062 and 8064 are controlled bysignals inputted though wires 8053 to 8056. Light emission/non-lightemission of the light-emitting element 8050 is controlled by a videosignal inputted though a wire 8051. Further, a power source is suppliedfrom a wire 8052 maintained at a certain potential to the above pixel.Note that the transistors included in the above pixel may be eithern-channel transistors or p-channel transistors.

Embodiment Mode 5

A pixel configuration which is different from the above embodiment modewill be described using FIG. 5B.

A pixel includes transistors 8160 to 8164, a capacitor 8165, and alight-emitting element 8150. The pixel may further include a capacitor8166. According to this pixel, one of a source and a drain of thetransistor 8160 and one of a first electrode and a second electrode ofthe light-emitting element 8150 are connected to the same wire 8159.

In the pixel shown in FIG. 5B, the transistors 8162 and 8163 and thecapacitors 8165 and 8166 correspond to the compensating circuit 106 inFIG. 1B.

ON/OFF of the transistors 8160 to 8162 are controlled by signalsinputted though wires 8153 to 8155. Light emission/non-light emission ofthe light-emitting element 8150 is controlled by a video signal inputtedthough a wire 8151. Further, a power source is supplied from a wire 8152maintained at a certain potential to the above pixel. Note that thetransistors included in the above pixel may be either n-channeltransistors or p-channel transistors.

Embodiment Mode 6

A pixel configuration which is different from the above embodiment modewill be described using FIG. 6A.

A pixel includes transistors 8210 to 8215, a capacitor 8216, and alight-emitting element 8200. The pixel may further include a capacitor8217. According to this pixel, one of a source and a drain of thetransistor 8210 and one of a first electrode and a second electrode ofthe light-emitting element 8200 are connected to the same wire 8209.

In the pixel shown in FIG. 6A, the transistor 8212 and the capacitors8216 and 8217 correspond to the compensating circuit 106 in FIG. 1B, andthe transistor 8214 corresponds to the controlling circuit 105 b in FIG.1B.

ON/OFF of the transistors 8210 to 8213 are controlled by signalsinputted though wires 8203 to 8205. Light emission/non-light emission ofthe light-emitting element 8200 is controlled by a video signal inputtedthough a wire 8201. Further, a power source is supplied from a wire 8202maintained at a certain potential to the above pixel. Note that thetransistors included in the above pixel may be either n-channeltransistors or p-channel transistors.

Embodiment Mode 7

A pixel configuration which is different from the above embodiment modewill be described using FIG. 6B.

A pixel includes transistors 8260 to 8262, a capacitor 8263, and alight-emitting element 8250. According to this pixel, one of a sourceand a drain of the transistor 8260 and one of a first electrode and asecond electrode of the light-emitting element 8250 are connected to thesame wire 8259.

In the pixel shown in FIG. 6B, the capacitor 8263 corresponds to thecompensating circuit 106 in FIG. 1B.

ON/OFF of the transistor 8261 is controlled by a signal inputted thougha wire 8253. Light emission/non-light emission of the light-emittingelement 8250 is controlled by a video signal inputted though a wire8251. Further, a power source is supplied from a wire 8252 maintained ata certain potential to the above pixel. Note that the transistorsincluded in the above pixel may be either n-channel transistors orp-channel transistors.

Embodiment Mode 8

A pixel configuration which is different from the above embodiment modewill be described using FIG. 7A.

A pixel includes transistors 8810 to 8814, capacitors 8815 and 8816, anda light-emitting element 8800. According to this pixel, one of a sourceand a drain of the transistor 8810 and one of a first electrode and asecond electrode of the light-emitting element 8800 are connected to thesame wire 8809.

In the pixel shown in FIG. 7A, the transistor 8812 and the capacitors8815 and 8816 correspond to the compensating circuit 106 in FIG. 1B, andthe transistor 8813 corresponds to the controlling circuit 105 a in FIG.1B.

ON/OFF of the transistors 8810 to 8813 are controlled by signalsinputted though wires 8803 to 8805. Light emission/non-light emission ofthe light-emitting element 8800 is controlled by a video signal inputtedthough a wire 8801. Further, a power source is supplied from a wire 8802maintained at a certain potential to the above pixel. Note that thetransistors included in the above pixel may be either n-channeltransistors or p-channel transistors.

Embodiment Mode 9

A pixel configuration which is different from the above embodiment modewill be described using FIG. 7B.

A pixel includes transistors 8360 to 8362, a capacitor 8363, and alight-emitting element 8350. According to this pixel, one of a sourceand a drain of the transistor 8360 and one of a first electrode and asecond electrode of the light-emitting element 8350 are connected to thesame wire 8359.

In the pixel shown in FIG. 7B, the capacitor 8363 corresponds to thecompensating circuit 106 in FIG. 1B.

ON/OFF of the transistor 8361 is controlled by a signal inputted thougha wire 8353. Light emission/non-light emission of the light-emittingelement 8350 is controlled by a video signal inputted though a wire8351. Further, a power source is supplied from a wire 8352 maintained ata certain potential to the above pixel. Note that the transistorsincluded in the above pixel may be either n-channel transistors orp-channel transistors.

Embodiment Mode 10

A pixel configuration which is different from the above embodiment modewill be described using FIG. 8A.

A pixel includes transistors 8410, 8411, 8413, and 8414, a capacitor8416, and a light-emitting element 8400. According to this pixel, one ofa source and a drain of the transistor 8410 and one of a first electrodeand a second electrode of the light-emitting element 8400 are connectedto the same wire 8409.

In the pixel shown in FIG. 8A, the transistor 8414 and the capacitor8416 correspond to the compensating circuit 106 in FIG. 1B, thetransistor 8413 corresponds to the controlling circuit 105 a in FIG. 1B,and the transistor 8415 corresponds to the controlling circuit 105 b inFIG. 1B.

ON/OFF of the transistors 8410 to 8415 are controlled by signalsinputted though wires 8403 to 8405. Light emission/non-light emission ofthe light-emitting element 8400 is controlled by a video signal inputtedthough a wire 8401. Further, a power source is supplied from a wire 8402maintained at a certain potential to the above pixel. Note that thetransistors included in the above pixel may be either n-channeltransistors or p-channel transistors.

Embodiment Mode 11

A pixel configuration which is different from the above embodiment modewill be described using FIG. 8B.

A pixel includes transistors 8460 to 8464, a capacitor 8465, and alight-emitting element 8450. According to this pixel, one of a sourceand a drain of the transistor 8460 and one of a first electrode and asecond electrode of the light-emitting element 8450 are connected to thesame wire 8459.

In the pixel shown in FIG. 8B, the transistor 8462 and the capacitor8465 correspond to the compensating circuit 106 in FIG. 1B, thetransistor 8463 corresponds to the controlling circuit 105 a in FIG. 1B.

ON/OFF of the transistors 8460 to 8462 are controlled by signalsinputted though wires 8453 to 8455. Light emission/non-light emission ofthe light-emitting element 8450 is controlled by a video signal inputtedthough a wire 8451. Further, a power source is supplied from a wire 8452maintained at a certain potential to the above pixel. Note that thetransistors included in the above pixel may be either n-channeltransistors or p-channel transistors.

Embodiment Mode 12

A pixel configuration which is different from the above embodiment modewill be described using FIG. 9A.

A pixel includes transistors 8510 to 8517, a capacitor 8518, and alight-emitting element 8500. According to this pixel, one of a sourceand a drain of the transistor 8510 and one of a first electrode and asecond electrode of the light-emitting element 8500 are connected to thesame wire 8509.

In the pixel shown in FIG. 9A, the transistors 8512 to 8514 and thecapacitor 8518 correspond to the compensating circuit 106 in FIG. 1B,the transistor 8515 corresponds to the controlling circuit 105 a in FIG.1B, and the transistor 8517 corresponds to the controlling circuit 105 bin FIG. 1B.

ON/OFF of the transistors 8510 to 8512, 8514, 8515, and 8517 arecontrolled by signals inputted though wires 8503 to 8507. Lightemission/non-light emission of the light-emitting element 8500 iscontrolled by a video signal inputted though a wire 8501. Further, apower source is supplied from a wire 8502 maintained at a certainpotential to the above pixel. Note that the transistors included in theabove pixel may be either n-channel transistors or p-channeltransistors.

Embodiment Mode 13

A pixel configuration which is different from the above embodiment modewill be described using FIG. 9B.

A pixel includes transistors 8560 to 8562, a capacitor 8563, and alight-emitting element 8550. According to this pixel, one of a sourceand a drain of the transistor 8560 and one of a first electrode and asecond electrode of the light-emitting element 8550 are connected to thesame wire 8559.

In the pixel shown in FIG. 9B, the capacitor 8563 corresponds to thecompensating circuit 106 in FIG. 1B.

ON/OFF of the transistors 8560 and 8561 are controlled by a signalinputted though a wire 8553. Light emission/non-light emission of thelight-emitting element 8550 is controlled by a video signal inputtedthough a wire 8551. Further, a power source is supplied from a wire 8552maintained at a certain potential to the above pixel. Note that thetransistors included in the above pixel may be either n-channeltransistors or p-channel transistors.

Embodiment Mode 14

A pixel configuration which is different from the above embodiment modewill be described using FIG. 10A.

A pixel includes switches 8610 to 8615, transistors 8617 and 8618, acapacitor 8619, and a light-emitting element 8600. According to thispixel, one of a source and a drain of the switch 8610 and one of a firstelectrode and a second electrode of the light-emitting element 8600 areconnected to the same wire 8609.

In the pixel shown in FIG. 10A, the transistor 8617, the switches 8613and 8614, and the capacitor 8619 correspond to the compensating circuit106 in FIG. 1A, the switch 8612 corresponds to the controlling circuit105 a in FIG. 1A, and the switch 8615 corresponds to the controllingcircuit 105 b in FIG. 1A.

One terminal of the switch 8611 is connected to a wire 8601, and oneterminal of the switch 8612 is connected to a wire 8602. Note that thetransistors included in the above pixel may be either n-channeltransistors or p-channel transistors.

Embodiment Mode 15

A pixel configuration which is different from the above embodiment modewill be described using FIG. 10B.

A pixel includes transistors 8660 to 8664, capacitors 8665 and 8666, anda light-emitting element 8650. The pixel may further include a capacitor8667. According to this pixel, one of a source and a drain of thetransistor 8660 and one of a first electrode and a second electrode ofthe light-emitting element 8650 are connected to the same wire 8659.

In the pixel shown in FIG. 10B, the transistors 8662 and 8663 and thecapacitors 8665 to 8667 correspond to the compensating circuit 106 inFIG. 1B.

ON/OFF of the transistors 8660 to 8662 are controlled by signalsinputted though wires 8654 to 8656. Light emission/non-light emission ofthe light-emitting element 8650 is controlled by a video signal inputtedthough a wire 8651. Further, a power source is supplied from wires 8652and 8653 each maintained at a certain potential to the above pixel. Notethat the transistors included in the above pixel may be either n-channeltransistors or p-channel transistors.

Embodiment Mode 16

A pixel configuration which is different from the above embodiment modewill be described using FIG. 11A.

A pixel includes transistors 8710 to 8715, a capacitor 8716, and alight-emitting element 8700. According to this pixel, one of a sourceand a drain of the transistor 8710 and one of a first electrode and asecond electrode of the light-emitting element 8700 are connected to thesame wire 8709.

In the pixel shown in FIG. 11A, the transistor 8713 and the capacitor8716 correspond to the compensating circuit 106 in FIG. 1B, thetransistor 8714 corresponds to the controlling circuit 105 a in FIG. 1B,and the transistor 8715 corresponds to the controlling circuit 105 b inFIG. 1B.

ON/OFF of the transistors 8710 and 8711, and 8713 to 8715 are controlledby signals inputted though wires 8703 and 8704. Light emission/non-lightemission of the light-emitting element 8700 is controlled by a videosignal inputted though a wire 8701. Further, a power source is suppliedfrom a wire 8702 maintained at a certain potential to the above pixel.Note that the transistors included in the above pixel may be eithern-channel transistors or p-channel transistors.

Embodiment Mode 17

A pixel configuration which is different from the above embodiment modewill be described using FIG. 11B.

A pixel includes transistors 8760 to 8764, a capacitor 8765, and alight-emitting element 8750. According to this pixel, one of a sourceand a drain of the transistor 8760 and one of a first electrode and asecond electrode of the light-emitting element 8750 are connected to thesame wire 8759.

In the pixel shown in FIG. 11B, the transistor 8762 and the capacitor8765 correspond to the compensating circuit 106 in FIG. 1B, and thetransistor 8764 corresponds to the controlling circuit 105 b in FIG. 1B.

ON/OFF of the transistors 8760, 8761, and 8764 are controlled by signalsinputted though wires 8753 and 8754. Light emission/non-light emissionof the light-emitting element 8750 is controlled by a video signalinputted though a wire 8751. Further, a power source is supplied from awire 8752 maintained at a certain potential to the above pixel. Notethat the transistors included in the above pixel may be either n-channeltransistors or p-channel transistors.

Embodiment Mode 18

In this embodiment mode, a display device to which the present inventionis applied will be described using FIGS. 13A and 13B.

FIG. 17A is a top view showing a structure of a display panel inaccordance with the present invention, where a pixel portion 2701 inwhich pixels 2702 are arranged in matrix, a scanning line side inputterminal 2703, and a signal line side input terminal 2704 are formedover a substrate 2700 having an insulating surface. The number of pixelsmay be provided according to various standards: the number of pixels ofXGA for RGB full-color display may be 1024×768×3 (RGB), that of UXGA forRGB full-color display may be 1600×1200×3 (RGB), and that correspondingto a full-speck high vision for RGB full-color display may be1920×1080×3 (RGB).

The pixels 2702 are arranged in matrix by intersecting scanning linesextended from the scanning line side input terminal 2703 with signallines extended from the signal line side input terminal 2704. Each pixel2702 is provided with a switching element and a pixel electrodeconnected to the switching element. A typical example of the switchingelement is a TFT. A gate electrode side of the TFT is connected to thescanning line, and a source or drain side thereof is connected to thesignal line; thereby each pixel can be controlled independently by asignal inputted from outside.

FIG. 17A shows a structure of the display panel in which signalsinputted to a scanning line and a signal line are controlled by anexternal driver circuit. Alternatively, driver ICs 2751 may be mountedon the substrate 2700 by COG (Chip on Glass) as shown in FIG. 18A.Further, the driver ICs may also be mounted by TAB (Tape AutomatedBonding) as shown in FIG. 18B. The driver ICs may be that formed over asingle crystal semiconductor substrate or may be a circuit which isformed using a TFT over a glass substrate. In FIGS. 18A and 18B, thedriver IC 2751 is connected to an FPC 2750.

Further, in the case where a TFT provided in a pixel is formed using apolycrystalline (microcrystalline) semiconductor having highcrystallinity, a scanning line side driver circuit 3702 can also beformed over a substrate 3700 as shown in FIG. 17B. In FIG. 18B,reference numeral 3701 denotes a pixel portion, and a signal line sidedriver circuit is controlled by an external driver circuit similarly tothat in FIG. 17A. In the case where a TFT provided in a pixel is formedusing a polycrystalline (microcrystalline) semiconductor, a singlecrystalline semiconductor, or the like with high mobility, a scanningline side driver circuit 4702 and a signal line side driver circuit 4704can be formed over the same substrate 4700 in FIG. 17C.

FIG. 13A is a top view of the display device described in thisembodiment mode, and a cross-sectional view taken along a line A-B inFIG. 13A is FIG. 13B. The display device in FIGS. 13A and 13B includesan external terminal connection region 302, a seal region 303, aperipheral driver circuit region 304 including a signal line drivercircuit, a peripheral driver circuit region 309, a peripheral drivercircuit region 307 including a scanning line driver circuit, aperipheral driver circuit region 308, and a connection region 305.

In this embodiment mode, the aforementioned circuits are provided;however, the present invention is not limited to this and an IC chip maybe mounted as a peripheral driver circuit by the aforementioned COG orTAB. Moreover, each of a scanning line driver circuit and a signal linedriver circuit may be provided in any number.

The display device shown in FIGS. 13A and 13B includes a substrate 300,thin film transistors 320 to 323, a first electrode 386, anelectroluminescent layer 388, a second electrode 389, a filling material393, a sealing material 392, insulating films 1311 a and 1311 b, a gateinsulating layer 312, insulating films 313 and 314, insulating layers315 and 316, a sealing substrate 395, wiring 385, 399, and 317, aterminal electrode layer 318, an anisotropic conductive layer 396, andan FPC 394. The display device includes the external terminal connectionregion 302, the seal region 303, the peripheral driver circuit region304, and a pixel region 306.

Each of the thin film transistors 320 to 323 has: a semiconductor layerincluding an impurity region functioning as either a source or a drain;the gate insulating layer 312; a gate electrode layer which has atwo-layer structure; and a wire which is in contact with the impurityregion which is either the source or the drain of the semiconductorlayer, to be electrically connected to each other.

The thin film transistor 320 is electrically connected to the firstelectrode 386 of a light-emitting element 390 via the wire 399 in thepixel region. The second electrode 389 of the light-emitting element 390is electrically connected to the wire 385 at an opening formed in theinsulating layer 316, and a wire connected to a source or a drain of thethin film transistor 321, which is formed in the insulating film 314,and the wire 385 are electrically connected to each other. The wire 385corresponds to the wire 109 in FIGS. 1A and 1B, and the second electrode389 of the light-emitting element 390 and the thin film transistor 321are electrically connected to each other via the wire 385.

If the number of wires which shut out light emitted from thelight-emitting element within the pixel is large, aperture ratio of thepixel is reduced in a bottom emission or dual emission display device.In the present invention, since the light-emitting element 390 and thethin film transistor 321 are connected in common to the same wireinstead of being connected to different wires each maintaining at acertain potential, a wire is not necessarily provided in plural numberwithin a pixel. Therefore, the number of wires within the pixel isreduced and the aperture ratio of the pixel can be improved.

Further, since dense disposition of wires can be prevented and the wirestructure does not become complex and dense in this structure, theprocess does not become complex. Therefore, shape defects by a complexprocess, pattern shape, or the like can be prevented, and a yield isimproved. Accordingly, a highly reliable display device can bemanufactured at a low cost with high productivity.

The substrate 300 may be a glass substrate, a quartz substrate, asilicon substrate, a metal substrate, or a stainless steel substratehaving a surface covered with an insulating film. Further, a plasticsubstrate which can resist a processing temperature of this embodimentmode or a flexible substrate such as a film may be used as well. As theplastic substrate, a substrate formed of PET (polyethyleneterephthalate), PEN (polyethylene naphthalate), or PES (polyethersulfonate) can be used, and a synthetic resin such as acrylic can beused as the flexible substrate.

Each of the insulating film 311 a which functions as a base film, theinsulating film 311 b, the gate insulating layer 312, the insulatingfilm 313, the insulating film 314, the insulating layer 315, and theinsulating layer 316 can be formed of either an inorganic insulatingmaterial or an organic insulating material. For example, an inorganicinsulating material such as silicon oxide, silicon nitride, siliconoxynitride, silicon nitride oxide, aluminum oxide, aluminum nitride, oraluminum oxynitride, or the like can be used. Alternatively, acrylicacid or methacrylic acid, a derivative thereof, a heat-resistant polymersuch as polyimide, aromatic polyamide, or polybenzimidazole, or siloxaneresin can be used. Note that a siloxane resin corresponds to a resinincluding a Si—O—Si bond. Siloxane has a skeletal structure with a bondof silicon (Si) and oxygen (O). As a substituent, an organic groupcontaining at least hydrogen (e.g., an alkyl group or aromatichydrocarbon) is used. Alternatively, a fluoro group may be used as thesubstituent, or both a fluoro group and an organic group containing atleast hydrogen may be used as the substituents. Alternatively, a resinmaterial such as a vinyl resin of polyvinyl alcohol, polyvinylbutyral,or the like, an epoxy resin, a phenol resin, a novolac resin, an acrylicresin, a melamine resin, or a urethane resin may be used. Further, anorganic material such as benzocyclobutene, parylene, flare, orpolyimide; a composition material containing a water-soluble homopolymerand a water-soluble copolymer; or the like may be used. Moreover,oxazole resin can also be used, which is, for example, photosensitivepolybenzoxazole. Photosensitive polybenzoxazole has a low dielectricconstant (a dielectric constant of 2.9 at normal temperature at 1 MHz),high heat resistance (TGA: Thermal Gravity Analysis) thermaldecomposition temperature of 550° C. with the rise in temperature at 5°C./min), and a low moisture absorbing rate (0.3% in 24 hours at normaltemperature).

Each insulating film (insulating layer) may be either a single-layer ora multi-layer such as two layers or three layers. Preferably, theinsulating layer 316, in particular, which functions as a partition wallhas a shape in which the radius of curvature is continuously varied, sothat coverage of the electroluminescent layer 388 and the secondelectrode 389 formed over the insulating layer 316 is improved.

Each of the insulating films (insulating layers) and the semiconductorlayer included in the thin film transistors 320 to 323 can be formed bysputtering, PVD (Physical Vapor Deposition), CVD (Chemical VaporDeposition) such as Low-pressure CVD (LPCVD) or plasma CVD, or the like.Further, a method using a liquid material such as a droplet dischargemethod, a printing method (a method for forming a pattern, such asscreen printing or offset printing), or a spin-coating method, a dippingmethod, a dispenser method, or the like can also be employed.

The semiconductor film (semiconductor layer) included in the thin filmtransistors 320 to 323 can be formed of the following material: anamorphous semiconductor (hereinafter also referred to as “AS”)manufactured by using a semiconductor material gas typified by silane orgermane by a vapor phase growth method or sputtering; a polycrystallinesemiconductor that is formed by crystallizing the amorphoussemiconductor by utilizing light energy or thermal energy; asemiamorphous (also referred to as microcrystal, and hereinafterreferred to as “SAS”) semiconductor; or the like. The semiconductorlayer can be formed by a known method (e.g., sputtering, LPCVD, orplasma CVD).

The SAS has an intermediate structure between an amorphous structure anda crystal structure (including a single crystalline structure and apolycrystalline structure), and a third condition that is stable in freeenergy, and further includes a crystalline region having a short rangeorder and lattice distortion. The SAS is formed by glow dischargedecomposition (plasma CVD) of silicide gas. As for the silicide gas,Si₂H₆, SiH₂Cl₂, SiHCl₃, SiCl₄, SiF₄, or the like can be used as well asSiH₄. Further, F₂ or GeF₄ may also be mixed. The silicide gas may alsobe diluted with H₂, or a mixture of H₂ and one or more of rare gaselements selected from He, Ar, Kr, and Ne. Further alternatively, as thesemiconductor layer, a multi-layer of a SAS layer formed from afluorine-based gas and a SAS layer formed from a hydrogen-based gas maybe used.

The amorphous semiconductor is typified by hydrogenated amorphoussilicon, and the crystalline semiconductor is typified by polysilicon.Polysilicon includes a so-called high-temperature polysilicon whichuses, as a main material, polycrystalline silicon formed at a processtemperature of 800° C. or more, a so-called low-temperature polysiliconwhich uses, as a main material, polycrystalline silicon formed at aprocess temperature of 600° C. or less, polysilicon which iscrystallized by adding an element for promoting crystallization or thelike, and the like. Of course, as described above, a semi-amorphoussemiconductor or a semiconductor which contains a crystalline phase in apart of the semiconductor layer can also be used.

As a material of the semiconductor, as well as a single substance suchas silicon (Si) or germanium (Ge), a compound semiconductor such asGaAs, InP, SiC, ZnSe, GaN, or SiGe can be used. In addition, zinc oxide(ZnO) or tin oxide (SnO₂) which is an oxide semiconductor can also beused. In the case of using ZnO for the semiconductor layer, a singlelayer or a multi-layer of Y₂O₃, Al₂O₃, or TiO₂ is preferably used as thegate insulating layer, and ITO, Au, Ti, or the like is preferably usedfor the gate electrode layer, a source electrode layer, or a drainelectrode layer. In addition, In, Ga, or the like can be added into ZnO.

In the case where a crystalline semiconductor layer is used as thesemiconductor layer, a known method (e.g., a laser crystallizationmethod, a thermal crystallization method, or a thermal crystallizationmethod using an element for promoting crystallization such as nickel)may be employed as a method of manufacturing the crystallinesemiconductor layer. Further, a microcrystalline semiconductor, which isa SAS, may be crystallized by being irradiated with laser light toimprove the crystallinity. In the case where an element for promotingcrystallization is not introduced, hydrogen is released until thehydrogen concentration in an amorphous semiconductor film becomes 1×10²⁰atoms/cm₃ or less by heating the amorphous semiconductor film at atemperature of 500° C. for one hour in a nitrogen atmosphere beforeirradiating the amorphous semiconductor film with laser light. This isbecause the amorphous semiconductor film containing much hydrogen isdamaged when the film is irradiated with laser light.

Any method can be used for introducing a metal element into theamorphous semiconductor layer as long as the metal element can exist onthe surface of or inside the amorphous semiconductor layer; for example,sputtering, CVD, a plasma treatment method (including plasma CVD), anadsorption method, or a method of applying a metal salt solution can beemployed. Among them, the method using a solution is advantageous insimplicity and easy concentration control of the metal element. At thistime, it is preferable to form an oxide film by UV light irradiation inan oxygen atmosphere, a thermal oxidation method, a treatment with ozonewater including hydroxyl radicals or hydrogen peroxide, or the like inorder to improve wettability of the surface of the amorphoussemiconductor layer and to spread the aqueous solution over the entiresurface of the amorphous semiconductor layer.

Further, in the crystallization step of crystallizing an amorphoussemiconductor layer to form a crystalline semiconductor layer, theamorphous semiconductor layer may be added an element for promotingcrystallization (also referred to as a catalytic element or a metalelement), and a thermal treatment (at 550° C. to 750° C. for 3 minutesto 24 hours) may be performed to crystallize the amorphous semiconductorlayer. As the element for promoting the crystallization, one or aplurality of elements selected from iron (Fe), nickel (Ni), cobalt (Co),ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir),platinum (Pt), copper (Cu), and gold (Au) can be used.

In order to remove or reduce the element for promoting crystallizationfrom the crystalline semiconductor layer, a semiconductor layercontaining an impurity element is formed in contact with the crystallinesemiconductor layer and used as a gettering sink. The impurity elementmay be an impurity element imparting n-type conductivity, an impurityelement imparting p-type conductivity, a rare gas element, or the like.For example, one or a plurality of elements selected from phosphorus(P), nitrogen (N), arsenic (As), antimony (Sb), bismuth (Bi), boron (B),helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe) can beused. In this embodiment mode, a semiconductor layer containing a raregas element is formed on the crystalline semiconductor layer containingthe element for promoting crystallization, and a thermal treatment (at550° C. to 750° C. for 3 minutes to 24 hours) is performed. The elementfor promoting crystallization in the crystalline semiconductor layermoves into the semiconductor layer containing the rare gas element,thereby the element for promoting crystallization in the crystallinesemiconductor layer is removed or reduced. After that, the semiconductorlayer containing the rare gas element, which functions as a getteringsink, is removed.

Thermal treatment and laser light irradiation may be combined tocrystallize the amorphous semiconductor layer; or only one of thethermal treatment or the laser light irradiation may be performed pluraltimes.

Alternatively, a crystalline semiconductor layer may be formed directlyon the substrate by a plasma method. Further, a crystallinesemiconductor layer may be selectively formed over the substrate by aplasma method.

An organic semiconductor material can be used as a semiconductor thereofby a printing method, a spray method, spin coating, a droplet dischargemethod, or the like. In this case, since the above etching step is notrequired, the number of steps can be reduced. A low molecular weightmaterial, a high molecular weight material, or the like is used for theorganic semiconductor, and a material such as an organic pigment or aconductive high molecular weight material can also be used. A π-electronconjugated high molecular weight material having a skeleton constitutedby a conjugated double bond is preferably used as the organicsemiconductor material. Typically, a soluble high molecular weightmaterial such as polythiophene, polyfluoren, poly(3-alkylthiophene), apolythiophene derivative or pentacene can be used.

Other than the above, a material with which a semiconductor layer can beformed by performing treatment after depositing a soluble precursor canbe used as the organic semiconductor material capable of being used inthe present invention. As such an organic semiconductor material, thereis polythienylenevinylene, poly(2,5-thienylenevinylene), polyacetyrene,a polyacetyrene derivative, polyallylenevinylene, or the like.

In converting the precursor to an organic semiconductor, a reactioncatalyst such as a hydrogen chloride gas is added in addition to a heattreatment. The following can be applied as a typical solvent fordissolving the soluble organic semiconductor material: toluene, xylene,chlorobenzene, dichlorobenzene, anisole, chloroform, dichloromethane,gamma butyl lactone, butyl cellosolve, cyclohexane, NMP(N-methyl-2-pyrrolidone), cyclohexanone, 2-butanone, dioxane,dimethylformamide (DMF), THF (tetrahydrofuran) or the like.

A gate electrode can be formed using CVD, sputtering, a dropletdischarge method, or the like. The gate electrode layer may be formed ofan element selected from Ag, Au, Cu, Ni, Pt, Pd, Ir, Rh, W, Al, Ta, Mo,Cd, Zn, Fe, Ti, Si, Ge, Zr, and Ba, or an alloy material or a compoundmaterial containing the above element as its main component. Further, asemiconductor layer typified by a polycrystalline silicon film dopedwith an impurity element such as phosphorus, or an Ag—Pd—Cu alloy mayalso be used. Either a single-layer structure or a multi-layer structuremay be employed. For example, a two-layer structure of a tungstennitride film and a molybdenum film or a three-layer structure in which atungsten film with a thickness of 50 nm, an alloy (Al—Si) film ofaluminum and silicon with a thickness of 500 nm, and a titanium nitridefilm with a thickness of 30 nm are sequentially stacked may be used.Further, in the case of the three-layer structure, tungsten nitride maybe used instead of the tungsten of the first conductive film, an alloy(Al—Ti) film of aluminum and titanium may be used instead of the alloy(Al—Si) film of aluminum and silicon of the second conductive film, anda titanium film may be used instead of the titanium nitride film of thethird conductive film.

A light-transmitting material having light-transmitting property tovisible light can also be used for the gate electrode. As thelight-transmitting conductive material, indium tin oxide (ITO), indiumtin oxide containing silicon oxide (ITSO), organic indium, organic tin,zinc oxide, or the like can be used. Further, indium zinc oxide (IZO)containing zinc oxide (ZnO), zinc oxide (ZnO), ZnO doped with gallium(Ga), tin oxide (SnO₂), indium oxide containing tungsten oxide, indiumzinc oxide containing tungsten oxide, indium oxide containing titanicoxide, indium tin oxide containing titanic oxide, or the like may beused as well.

If etching processing is required to form the gate electrode, a mask maybe formed and dry etching or wet etching may be performed. The electrodelayer can be etched into a tapered shape by using an ICP (InductivelyCoupled Plasma) etching method and appropriately adjusting the etchingcondition (e.g., the amount of electric power applied to a coiledelectrode, the amount of electric power applied to an electrode on asubstrate side, or the temperature of the electrode on the substrateside). As the etching gas, a chlorine-based gas typified by Cl₂, BCl₃,SiCl₄, CCl₄, or the like; a fluorine-based gas typified by CF₄, SF₆,NF₃, or the like; or O₂ can be arbitrarily used.

In addition, even after the substrate, the insulating layer, thesemiconductor layer, the gate insulating layer, the interlayerinsulating layer, another insulating layer or conductive layer or thelike for structuring a display device is formed, a surface of thesubstrate, the insulating layer, the semiconductor layer, the gateinsulating layer, or the interlayer insulating layer may be oxidized ornitrided by performing oxidizing or nitriding with plasma treatment. Ifa semiconductor layer or an insulating layer is oxidized or nitridedwith plasma treatment, a surface of the semiconductor layer or theinsulating layer is modified, and a semiconductor layer or an insulatinglayer which is much denser can be obtained, compared with that formed byCVD or sputtering. Thus, a defect such as a pinhole can be suppressed sothat characteristics or the like of the display device can be improved.In addition, the conductive layer such as the gate electrode or the wirecan also be subjected to the above-described plasma treatment, and asurface thereof can be nitrided or oxidized by the nitriding oroxidizing (or both of them).

The plasma treatment is performed in the above gas atmosphere with anelectron density of 1×10¹¹ cm⁻³ or more and a plasma electrontemperature of 1.5 eV or less. More specifically, the plasma treatmentis performed with an electron density of 1×10¹¹ cm⁻³ or more and 1×10¹³cm⁻³ or less, and a plasma electron temperature of 0.5 eV or more and1.5 eV or less. Since the plasma electron density is high and theelectron temperature around an object to be processed formed over thesubstrate is low, damage by plasma to the object to be processed can beprevented. In addition, since the plasma electron density is as high as1×10¹¹ cm⁻³ or more, an oxide film or a nitride film formed by oxidizingor nitriding the object with the plasma treatment has better uniformityin thickness and the like and is denser, compared with a film formed byCVD, sputtering, or the like. In addition, since the plasma electrontemperature is as low as 1.5 eV or less, oxidizing or nitridingtreatment can be performed at a lower temperature than a conventionalplasma treatment or a thermal oxidation method. For example, even whenplasma treatment is performed at a temperature lower than a distortionpoint of a glass substrate by 100° C. or more, the oxidizing treatmentor the nitriding treatment can be performed sufficiently. As forfrequency for generating plasma, a high frequency wave such as amicrowave (2.45 GHz) can be used. Note that the above conditions areused for plasma treatment, if not otherwise specified hereinafter.

Although a single gate structure is described in this embodiment mode, amulti-gate structure such as a double-gate structure may also beemployed. In this case, gate electrode layers may be provided above andbelow the semiconductor layer or a plurality of gate electrode layersmay be provided only on one side (above or below) of the semiconductorlayer. The semiconductor layer may have impurity regions havingdifferent concentrations. For example, the vicinity of a channel regionof the semiconductor layer, where the gate electrode layer is stacked,may be a low-concentration impurity region, and the region outside thelow-concentration impurity region may be a high-concentration impurityregion.

Each of the wires connected to the thin film transistors 320 to 323, thewire 385, the wire 399, the wire 317, and the terminal electrode layer318 can be formed as follows: a conductive film is formed by PVD, CVD,vapor deposition, or the like, and then is etched to be a desired shape.Further, the source electrode layer or the drain electrode layer can beselectively formed at a predetermined position by a printing method, anelectric plating method, or the like. Alternatively, a reflow method ora damascene method may be used. As a material of the source electrodelayer or the drain electrode layer, an metal such as Ag, Au, Cu, Ni, Pt,Pd, Ir, Rh, W, Al, Ta, Mo, Cd, Zn, Fe, Ti, Zr, or Ba; or a semiconductorsuch as Si or Ge or an alloy thereof, or nitride thereof may be used. Inaddition, a light-transmitting material can also be used.

Further, as the light-transmitting conductive material, indium tin oxide(ITO), indium tin oxide containing silicon oxide (ITSO), indium zincoxide (IZO) containing zinc oxide (ZnO), zinc oxide (ZnO), ZnO dopedwith gallium (Ga), tin oxide (SnO₂), indium oxide containing tungstenoxide, indium zinc oxide containing tungsten oxide, indium oxidecontaining titanic oxide, indium tin oxide containing titanic oxide, orthe like can be used as well.

The first electrode 386 (also called a pixel electrode) functions as ananode or a cathode. As the first electrode layer 386, a film containingas its main component an element selected from Ti, Ni, W, Cr, Pt, Zn,Sn, In, and Mo, or an alloy material or a compound material containingthe aforementioned element as a main component, such as TiN,TiSi_(X)N_(Y), WSi_(X), WN_(X), WSi_(X)N_(Y), or NbN, or a multi-layerthereof with a total thickness of 100 to 800 nm may be used.

Further, a transparent conductive film formed of a light-transmittingconductive material can also be used as the first electrode layer 386;indium oxide containing tungsten oxide, indium zinc oxide containingtungsten oxide, indium oxide containing titanium oxide, indium tin oxidecontaining titanium oxide, or the like can be used. Of course, indiumtin oxide (ITO), indium zinc oxide (IZO), indium tin oxide doped withsilicon oxide (ITSO), or the like can also be used.

An example of a composition ratio in each light-transmitting conductivematerial will be described. In the composition ratio of indium oxidecontaining tungsten oxide, tungsten oxide may be 1.0 wt % and indiumoxide may be 99.0 wt %. In the composition ratio of indium zinc oxidecontaining tungsten oxide, tungsten oxide may be 1.0 wt %, zinc oxidemay be 0.5 wt %, and indium oxide may be 98.5 wt %. In the compositionratio of indium oxide containing titanium oxide, titanium oxide may be1.0 to 5.0 wt % and indium oxide may be 99.0 to 95.0 wt %. In thecomposition ratio of indium tin oxide (ITO), tin oxide may be 10.0 wt %and indium oxide may be 90.0 wt %. In the composition ratio of indiumzinc oxide (IZO), zinc oxide may be 10.7 wt % and indium oxide may be89.3 wt %. Further, in the composition ratio of indium tin oxidecontaining titanium oxide, titanium oxide may be 5.0 wt %, tin oxide maybe 10.0 wt %, and indium oxide may be 85.0 wt %. The composition ratiosas described above are just examples, and the composition ratio may beset as appropriate.

Further, even in the case where a non-light-transmitting material suchas a metal film is used for the first electrode 386, when the thicknessis made thin (preferably, about 5 to 30 nm) so as to be able to transmitlight, light can be emitted through the first electrode layer 386. Asthe metal thin film capable of being used for the first electrode 386, aconductive film formed of titanium, tungsten, nickel, gold, platinum,silver, aluminum, magnesium, calcium, lithium, or an alloy thereof canbe used.

The first electrode 386 can be formed using a evaporation method,sputtering, CVD, printing, a dispenser method, a droplet dischargemethod, or the like.

The first electrode 386 may be cleaned and polished with CMP and apolyvinyl alcohol porous body in order to flat its surface. Further,after polishing by CMP, UV ray irradiation, oxygen plasma treatment orthe like may be performed to the surface of the first electrode 386.

A heat treatment may be performed after forming the first electrodelayer 386. With this heat treatment, moisture contained in the firstelectrode 386 is released. Accordingly, since degasification or the likedoes not occur from the first electrode 386, even when a light-emittingmaterial which is easily deteriorated by moisture is formed over thefirst electrode, the light-emitting material is not deteriorated;therefore, a high reliable display device can be manufactured.

The electroluminescent layer 388 can be selectively formed using amaterial which shows luminescence of color red (R), green (G) or blue(B), by an evaporation method using a deposition mask, or the like.Alternatively, the electroluminescent layer may be formed using amaterial which shows luminescence of color white (W). The materialswhich show luminescence of color red (R), green (G) and blue (B) (e.g.,a low molecular or high molecular weight material) can also be formed bya droplet discharge method; this case is preferable in that separatecoating of RGB can be carried out without using a mask.

The second electrode 389 can be formed of: Al, Ag, Li, Ca; an alloy or acompound thereof such as MgAg, MgIn, AlLi, CaF₂; calcium nitride; or thelike.

An insulating layer may be provided over the second electrode 389, as apassivation film (protective film). To thus provide the passivation filmso as to cover the second electrode 389 is effective. The passivationfilm is structured by an insulating film containing silicon nitride,silicon oxide, silicon oxynitride, silicon nitride oxide, aluminumnitride, aluminum oxynitride, aluminum nitride oxide of which nitrogencontent is larger than oxygen content, aluminum oxide, diamond likecarbon (DLC), or a carbon film containing nitrogen, with a single-layerstructure or a multi-layer structure thereof. Further, a siloxane resinmay also be used.

In this case, it is preferable to use a film with good coverage as thepassivation film, and a carbon film, particularly a DLC film, iseffective. Since a DLC film can be formed at temperatures ranging fromroom temperature to 100° C. or less, it can be easily formed even overthe electroluminescent layer 388 with low heat resistance. A DLC filmcan be formed by a plasma CVD method (typically, an RF plasma CVDmethod, a microwave CVD method, an electron cyclotron resonance (ECR)CVD method, a hot-filament CVD method, or the like), a combustion flamemethod, a sputtering method, an ion beam vapor deposition method, alaser vapor deposition method, or the like. As a reaction gas fordeposition, a hydrogen gas and a hydrocarbon-based gas (e.g., CH₄, C₂H₂,or C₆H₆) are used and ionized by glow discharge, and then deposition iscarried out with accelerative collision of ions with a cathode to whicha negative self-bias is applied. In addition, the CN film may be formedby using C₂H₄ gas and N₂ gas as reaction gases. A DLC film has highblocking effect to oxygen and thus can suppress oxidation of theelectroluminescent layer 388. Therefore, a problem of oxidation of theelectroluminescent layer 388 during a subsequent sealing step can beprevented.

The light-emitting element is sealed by bonding the substrate 300 wherethe light-emitting element 390 is formed to the sealing substrate 395with the sealing material 392. As the sealing material 392, a visiblelight curing, ultraviolet curing or thermosetting resin is preferablyused. For example, an epoxy resin such as a bisphenol A liquid resin, abisphenol A solid resin, a resin containing bromo-epoxy, a bisphenol Fresin, a bisphenol AD resin, a phenol resin, a cresol resin, a novolacresin, a cyclic aliphatic epoxy resin, an epibis epoxy resin, a glycidylester resin, a glycidyl amine resin, a heterocyclic epoxy resin, or amodified epoxy resin can be used. Note that a region surrounded with thesealing material may be filled with a filler 393, and nitrogen or thelike may be encapsulated therein by sealing the light-emitting elementin a nitrogen atmosphere. The filler 393 does not necessarily havelight-transmitting property in the case of a bottom emission type,whereas in the case of a structure in which light is extracted throughthe filler 393, the filler needs to have light-transmitting property.Typically, a visible light curing, ultraviolet curing, or thermosettingepoxy resin may be used. Through the above-described steps, a displaydevice having a display function using a light-emitting element in thisembodiment mode is completed. Further, the filler in a liquid state maybe dropped and can fill the inside of the display device. If ahygroscopic material such as a drying agent is used as the filler, amoisture absorption effect is further obtained and deterioration of anelement can be prevented.

A drying agent is provided within the display device in order to preventdeterioration of an element due to moisture. In this embodiment mode,the drying agent is provided in a concave portion formed to surround thepixel region in the sealing substrate, so as not to hinder thinning ofthe display device. In addition, a drying agent may also be provided ina region corresponding to a wire to increase the area of moistureabsorption, which leads to high absorption efficiency. Further, sincethe drying agent is provided on the wire that does not emit lightitself, the light-extraction efficiency is not reduced.

Note that this embodiment mode shows the case where the light-emittingelement is sealed with the glass substrate. The sealing treatment is atreatment to protect the light-emitting element from moisture.Therefore, any of a method in which a light-emitting element ismechanically sealed with a cover material, a method in which alight-emitting element is sealed with a thermosetting resin or anultraviolet curing resin, and a method in which a light-emitting elementis sealed with a thin film of metal oxide, metal nitride, or the likehaving high barrier capability, can be used. As for the cover material,glass, ceramics, plastic, or metal can be used; however, when light isemitted to the cover material side, the cover material needs to havelight-transmitting property. Enclosed space is formed by attaching thecover material to the substrate where the above-mentioned light-emittingelement is formed with a sealing material such as a thermosetting resinor an ultraviolet curing resin and then by curing the resin with athermal treatment or an ultraviolet irradiation treatment. It is alsoeffective to provide a hydroscopic material typified by barium oxide inthe enclosed space. The hydroscopic material may be provided on thesealing material or over a partition wall or in the peripheral partthereof so as not to block light emitted from the light-emittingelement. Further, it is also possible to fill the space between thecover material and the substrate where the light-emitting element isformed with a thermosetting resin or an ultraviolet curing resin. Inthis case, it is effective to add a hydroscopic material typified bybarium oxide in the thermosetting resin or the ultraviolet curing resin.

If the number of wires which shut out light emitted from thelight-emitting element within the pixel is large, aperture ratio of thepixel is reduced in a bottom emission or dual emission display device.In the present invention, since the light-emitting element 390 and thethin film transistor 321 are connected in common to the same wireinstead of being connected to different wires each maintaining at acertain potential, a wire is not necessarily provided in plural numberwithin a pixel. Therefore, the number of wires within the pixel isreduced and the aperture ratio of the pixel can be improved.

Further, since dense disposition of wires can be prevented and the wirestructure does not become complex and dense in this structure, theprocess does not become complex. Therefore, shape defects by a complexprocess, pattern shape, or the like can be prevented, and a yield isimproved. Accordingly, a highly reliable display device can bemanufactured at a low cost with high productivity.

This embodiment mode can be combined with each of Embodiment Modes 1 to17.

Embodiment Mode 19

A display device having a light-emitting element can be formed using thepresent invention, and one of top emission, bottom emission, and dualemission of light from the light-emitting element is performed. As forthe light emitted from the light-emitting element, the light isextracted from the substrate where the element is provided in the caseof the bottom emission, the light is emitted from the sealing substrateside in the case of the top emission, and the light is emitted from bothof the substrates interposing the light-emitting element therebetween inthe case of the dual emission. Here, a stack structure of thelight-emitting element depending on each case will be described usingFIGS. 16A to 16C.

In this embodiment mode, the case where an inversely staggered thin filmtransistor is used as a thin film transistor in a pixel will bedescribed. The transistor capable of being used in the present inventionis not particularly limited; either a top-gate transistor or abottom-gate transistor as described in this embodiment mode may be used.There are channel etch type and channel protection type in an inverselystaggered thin film transistor; and in this embodiment mode, the casewhere a channel protection type, inversely staggered thin filmtransistor having a channel protection layer is used will be described.Further, in the case described in this embodiment mode, an insulatinglayer which functions as a partition wall is formed over the transistorand an interlayer insulating layer is not formed between the transistorand the partition wall.

In the present invention, a conductive layer for forming a wire layer oran electrode layer, a mask layer for forming a predetermined pattern, orthe like may be formed by a method of forming a pattern selectively,such as a droplet discharge method. By the droplet discharge (jet)method (also called an inkjet method according to the system thereof), apredetermined pattern (a conductive layer, an insulating layer or thelike) can be formed by selectively discharging (jetting) liquid dropletsof a composition prepared for a specific purpose. In this case, aprocess for controlling wettability or adhesion may be performed to theformation region. Further, a method for transferring or drawing apattern, for example, a printing method (a method of forming a pattern,e.g., screen printing or offset printing), dispenser method, or the likecan also be used.

In the case of forming a film (e.g., an insulating film or a conductivefilm) by a droplet discharge method, the film is formed as follows: acomposition containing a film material which is processed into aparticle form is discharged, and the composition is fused or welded bybaking to be solidified. A film formed by a sputtering method or thelike tends to have a columnar structure, whereas the film thus formed bydischarging and baking the composition containing a conductive materialtends to have a polycrystalline structure having a large number of grainboundaries. Further, since the film in a fluid liquid state is attachedto the formation region, the film may have a smooth surface havingcurvature in accordance with the shape of the liquid state.

A droplet discharge means used in a droplet discharge method has a meansfor discharging liquid droplets, which includes a nozzle equipped with acomponent discharge outlet, a head having one or a plurality of nozzles,or the like. Each nozzle of the droplet discharge means is set that thediameter is 0.02 to 100 μm (preferably 30 μm or less) and the quantityof component discharge is 0.001 to 100 pl (preferably 0.1 pl or more and40 pl or less, and more preferably 10 pl or less). The dischargequantity is increased proportionately to the diameter of the nozzle. Itis preferable that a distance between an object to be processed and thedischarge outlet of the nozzle be as short as possible in order to dropon a desired position; the distance is preferably set to be 0.1 to 3 mm(more preferably 1 mm or less).

As the composition to be discharged from the discharge outlet, aconductive material dissolved or dispersed in a solvent is used. Theconductive material corresponds to a fine particle or a dispersednanoparticle of metal such as Ag, Au, Cu, Ni, Pt, Pd, Ir, Rh, W, or Al,and sulfide of metal such as Cd or Zn, oxide of Fe, Ti, Si, Ge, Zr, Ba,or the like, a fine particle or a dispersed nanoparticle of silverhalide, or the like may be mixed. In addition, the above-describedconductive materials may also be used in combination. For a transparentconductive film, indium tin oxide (ITO), indium tin oxide containingsilicon oxide (ITSO), organic indium, organic tin, zinc oxide (ZnO),titanium nitride, or the like can be used. Further, indium zinc oxide(IZO) containing zinc oxide, ZnO doped with gallium (Ga), tin oxide(SnO₂), indium oxide containing tungsten oxide, indium zinc oxidecontaining tungsten oxide, indium oxide containing titanium oxide,indium tin oxide containing titanium oxide, or the like may also beused. However, as for the composition to be discharged from thedischarge outlet, it is preferable to use one of the materials of gold,silver, and copper dissolved or dispersed in a solvent, considering aspecific resistance value; it is more preferable to use silver or copperhaving a low resistance value. When silver or copper is used, however, abarrier film may be preferably provided in addition as a countermeasureagainst impurities. A silicon nitride film or a nickel boron (NiB) filmcan be used as the barrier film.

The composition to be discharged is a conductive material dissolved ordispersed in a solvent, which further contains a dispersant, or athermosetting resin called a binder. In particular, the binder has afunction to prevent generation of cracks or uneven shape change duringbaking. Thus, a formed conductive layer may contain an organic material.The organic material to be contained depends on heating temperature,atmosphere, and time. This organic material is an organic resin whichfunctions as a binder, a solvent, a dispersant, and a coating of a metalparticle, or the like; polyimide, acrylic, a novolac resin, a melamineresin, a phenol resin, an epoxy resin, a silicon resin, a furan resin, adiallyl phthalate resin, and the like can be give as examples of theorganic material.

In addition, a particle with a plurality of layers, in which aconductive material is coated with another conductive material, may alsobe used. For example, a particle with a three-layer structure in whichcopper is coated with nickel boron (NiB) and the nickel boron is furthercoated with silver, may be used. As for the solvent, esters such asbutyl acetate or ethyl acetate, alcohols such as isopropyl alcohol orethyl alcohol, an organic solvent such as methyl ethyl ketone oracetone, water, or the like is used. The viscosity of the composition ispreferably 20 mPa·s (cp) or less; this prevents the composition fromdrying, and enables the composition to be discharged smoothly from thedischarge outlet. The surface tension of the composition is preferably40 mN/m or less. However, the viscosity of the composition and the likemay be appropriately controlled depending on a solvent to be used and anintended purpose. For example, the viscosity of a composition in whichITO, organic indium, or organic tin is dissolved or dispersed in asolvent may be set to be 5 mPa·s to 20 mPa·s, the viscosity of acomposition in which silver is dissolved or dispersed in a solvent maybe set to be 5 mPa·s to 20 mPa·s, and the viscosity of a composition inwhich gold is dissolved or dispersed in a solvent may be set to be 5mPa·s to 20 mPa·s.

Further, the conductive layer may also be formed by stacking a pluralityof conductive materials. In addition, the conductive layer may be formedfirst by a droplet discharge method using silver as a conductivematerial, and may then be plated with copper or the like. The platingmay be performed by an electroplating or chemical (electroless) platingmethod. The plating may be performed by immersing a substrate surface ina container filled with a solution containing a plating material;alternatively, the solution containing a plating material may be appliedto the substrate placed obliquely (or vertically) so as to flow thesolution containing a plating material on the substrate surface. Whenthe plating is performed by applying a solution to the substrate placedobliquely (or vertically), there is the advantage of miniaturizing aprocess apparatus.

The diameter of a particle of the conductive material is preferably assmall as possible, for the purpose of preventing nozzles from beingclogged and for manufacturing a minute pattern, although it depends onthe diameter of each nozzle, a desired shape of a pattern, and the like.Preferably, the diameter of the particle of the conductive material is0.1 μm or less. The composition is formed by a method such as anelectrolyzing method, an atomizing method, or a wet reduction method,and the particle size is generally about 0.01 μm to 10 μm. However, whena gas evaporation method is employed, nanoparticles protected by adispersant are as minute as about 7 nm, and when the surface of eachparticle is covered with a coating, the nanoparticles do not aggregatein the solvent and are uniformly dispersed in the solvent at roomtemperature, and behaves similarly to a liquid. Accordingly, it ispreferable to use a coating.

In addition, the step of discharging the composition may be performedunder reduced pressure. When the step is performed under reducedpressure, an oxide film or the like is not formed on the surface of theconductive layer, which is preferable. After discharging thecomposition, either or both steps of drying and baking are performed.Both the drying step and baking step are thermal treatment; however,drying is performed for three minutes at 100° C. and baking is performedfor 15 minutes to 60 minutes at 200° C. to 350 C.° for example, and theyare different in purpose, temperature, and time period. The steps ofdrying and baking are performed under normal pressure or under a reducedpressure, by laser light irradiation, rapid thermal annealing, heatingusing a heating furnace, or the like. Note that the timing of each heattreatment is not particularly limited. The substrate may be heated inadvance to favorably perform the steps of drying and baking, and thetemperature of the substrate at that time is, although it depends on thematerial of the substrate or the like, generally 100° C. to 800° C.(preferably, 200° C. to 350° C.). Through these steps, nanoparticles aremade in contact with each other and fusion and welding are acceleratedby hardening and shrinkage of a peripheral resin while volatilizing thesolvent in the composition or chemically removing the dispersant.

A continuous wave or pulsed gas laser or solid-state laser may be usedfor laser light irradiation. An excimer laser, a YAG laser, or the likecan be used as the former gas laser. A laser using a crystal of YAG,YVO₄, GdVO₄, or the like which is doped with Cr, Nd, or the like can beused as the latter solid-state laser, for example. Note that it ispreferable to use a continuous wave laser in consideration of theabsorptance of laser light. Moreover, a laser irradiation method inwhich pulsed and continuous wave lasers are combined may be used.However, it is preferable that the heat treatment by laser lightirradiation is instantaneously performed within several microseconds toseveral tens of seconds so as not to damage the substrate, depending onheat resistance of the substrate. Rapid thermal annealing (RTA) iscarried out by raising the temperature rapidly and heatinginstantaneously for several microseconds to several minutes with the useof an infrared lamp or a halogen lamp which emits ultraviolet toinfrared light in an inert gas atmosphere. Since this treatment isperformed instantaneously, only an outermost thin film can besubstantially heated and the lower layer of the film is not affected. Inother words, even a substrate having a low heat resistance such as aplastic substrate is not affected.

After forming the object by discharging a liquid composition by adroplet discharge method, the surface thereof may be planarized bypressing with pressure to improve planarity. As a pressing method,concavity and convexity may be reduced by moving a roller-shaped objecton the surface, or the surface may be perpendicularly pressed with aflat plate-shaped object. A heating step may be performed at the time ofpressing. Alternatively, the concavity and convexity of the surface maybe eliminated with an air knife after softening or melting the surfacewith a solvent or the like. A CMP method may also be used for polishingthe surface. This step can be employed in planarizing a surface whenconcavity and convexity are generated by the droplet discharge method.

Although the film formation method by the above-described dropletdischarge method is described using the case of a conductive layer as anexample, the conditions for discharge, drying, baking, a solvent, or thelike and the detailed explanation can also be applied to the insulatinglayer formed in this embodiment mode. By combining a droplet dischargemethod, cost can be reduced as compared to the case of entire surfacecoating by a spin coating method or the like.

FIGS. 16A to 16C are cross-sectional views for showing a light-emittingelement and a transistor which functions as a driving transistorconnected to the light-emitting element; light from the light-emittingelement is emitted in a direction denoted by an arrow. The substrateused for sealing is omitted in FIGS. 16A to 16C.

In pixels of FIGS. 16A to 16C, transistors 481, 461, and 471 areinversely staggered thin film transistors which are similarlymanufactured. Therefore, although the transistor 481 will be describedas an example, the transistors 461 and 471 each have the same structure.

The transistor 481 is provided over a substrate 480 havinglight-transmitting property, and is structured by a gate electrode layer493, a gate insulating film 497, a semiconductor layer 494, asemiconductor layer 495 a having n-type conductivity, a semiconductorlayer 495 b having n-type conductivity, a source electrode layer or adrain electrode layer 487 a, the source electrode layer or the drainelectrode layer 487 b, and a channel protection layer 496.

In this embodiment mode, a crystalline semiconductor layer is used asthe semiconductor layer, and a semiconductor layer having n-typeconductivity is used as the semiconductor layer having one conductivitytype. Instead of forming a semiconductor layer having n-typeconductivity, plasma treatment using a PH₃ gas may be performed toprovide conductivity for the semiconductor layer. The semiconductorlayer is not limited to that described in this embodiment mode; anamorphous semiconductor layer may be used. In the case of using acrystalline semiconductor layer of polysilicon or the like as is in thisembodiment mode, an impurity region having one conductivity type may beformed by introducing (adding) impurities into the crystallinesemiconductor layer without forming the semiconductor layer having oneconductivity type. Further, an organic semiconductor such as pentacenecan be used; if an organic semiconductor is selectively formed by adroplet discharge method or the like, the etching process to form adesired shape can be simplified.

In this embodiment mode, an amorphous semiconductor layer iscrystallized to form a crystalline semiconductor layer as thesemiconductor layer 494. In the crystallization process, the amorphoussemiconductor layer is crystallized by being added with an element forpromoting crystallization (also referred to as a catalytic element or ametal element), and performing a heat treatment (at 550° C. to 750° C.for 3 minutes to 24 hours). As the element for promotingcrystallization, metal elements for promoting crystallization of siliconcan be used, such as one or more of iron (Fe), nickel (Ni), cobalt (Co),ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir),platinum (Pt), copper (Cu), and gold (Au), and nickel is used in thisembodiment mode.

In order to remove or reduce the element for promoting crystallizationfrom the crystalline semiconductor layer, a semiconductor layercontaining an impurity element is formed in contact with the crystallinesemiconductor layer and functioned as a gettering sink. The impurityelement may be an n-type impurity element, a p-type impurity element, ora rare gas element; for example, one or more of phosphorus (P), nitrogen(N), arsenic (As), antimony (Sb), bismuth (Bi), boron (B), helium (He),neon (Ne), argon (Ar), Kr (Krypton), and Xe (Xenon) can be used. In thisembodiment mode, as the semiconductor layer containing the impurityelement that functions as the gettering sink, a semiconductor layerhaving n-type conductivity, which contains phosphorus (P) that is ann-type impurity element, is formed. The semiconductor layer havingn-type conductivity is formed on the crystalline semiconductor layercontaining the element for promoting crystallization, and a thermaltreatment is performed (at 550° C. to 750° C. for 3 minutes to 24hours). The element for promoting crystallization contained in thecrystalline semiconductor layer moves into the semiconductor layerhaving n-type conductivity. Accordingly, the element for promotingcrystallization in the crystalline semiconductor layer is removed orreduced, thereby the semiconductor layer 494 is formed. Meanwhile, thesemiconductor layer having n-type conductivity becomes a semiconductorlayer having n-type conductivity which contains the metal element forpromoting crystallization, and then the shape is processed to be thesemiconductor layers 495 a and 495 b having n-type conductivity. Asdescribed above, the semiconductor layer having n-type conductivityfunctions both as the gettering sink of the semiconductor layer 494 andas the source or drain region.

In this embodiment mode, the crystallization process and the getteringprocess of the semiconductor layer are performed by a plurality of heattreatments. However, the crystallization process and the getteringprocess can also be performed by one heat treatment. In this case, aheat treatment may be performed after forming an amorphous semiconductorlayer, adding an element for promoting crystallization, and forming asemiconductor layer which functions as a gettering sink.

In this embodiment mode, after the gate insulating layer is formed bystacking a plurality of layers, a silicon nitride oxide film and asilicon oxynitride film are stacked on the gate electrode layer 493side, as the gate insulating film 497 having a two-layer structure. Theinsulating layer is preferably formed by successively forming the layersat the same temperature in the same chamber while changing reactiongases with a vacuum state maintained. When the films are successivelyformed while maintaining the vacuum state, interfaces between thestacked films can be prevented from being contaminated.

The channel protection layer 496 may be formed by a droplet dischargemethod using polyimide, polyvinyl alcohol or the like. As a result, alight exposure process can be omitted. The channel protection layer maybe formed of one or more of an inorganic material (e.g., silicon oxide,silicon nitride, silicon oxynitride, or silicon nitride oxide), aphotosensitive or non-photosensitive organic material (e.g., an organicresin material) (e.g., polyimide, acrylic, polyamide, polyimide amide,or benzocyclobutene), a resist, a low dielectric constant material andthe like, or a multi-layer thereof or the like. In addition, a siloxaneresin material may also be used. As a manufacturing method, a vaporphase growth method such as a plasma CVD method or a thermal CVD method,or a sputtering method can be used. A droplet discharge method or aprinting method (a method for forming a pattern, such as screen printingor offset printing) can also be used. A thin film obtained by aspin-coating method can also be used.

First, the case where light is emitted to the substrate 480 side, thatis the case of bottom emission will be described using FIG. 16A. In thiscase, a first electrode layer 484, an electroluminescent layer 485, anda second electrode layer 486 are stacked sequentially in contact withthe source electrode layer or the drain electrode layer 487 b so as tobe electrically connected to the transistor 481. The substrate 480through which light is transmitted is required at least to havelight-transmitting property to visible light. Next, the case where lightis emitted to the opposite side to a substrate 460, that is the case oftop emission will be described using FIG. 16B. The transistor 461 can beformed similarly to the above-described thin film transistor.

A source electrode layer or drain electrode layer 462 that iselectrically connected to the transistor 461 is in contact with a firstelectrode layer 463 to be electrically connected to each other. Thefirst electrode layer 463, an electroluminescent layer 464 and a secondelectrode layer 465 are sequentially stacked. The source electrode layeror drain electrode layer 462 is a metal layer having reflexivity, andreflects light which is emitted from the light-emitting element, upwardas denoted by an arrow. The source electrode layer or drain electrodelayer 462 has a structure stacked on the first electrode layer 463, andtherefore, even when the first electrode layer 463 is formed of amaterial having light-transmitting property and transmits light, thelight is reflected on the source electrode layer or drain electrodelayer 462 and then is emitted in the direction opposite to the substrate460 side. Needless to say, the first electrode layer 463 may also beformed using a metal film having reflexivity. Since light from thelight-emitting element is emitted through the second electrode layer465, the second electrode layer 465 is formed using a material havinglight-transmitting property at least in a visible region.

The case where light is emitted to the substrate 470 side and to theside opposite to the substrate 470 side, that is the case of dualemission will be described using FIG. 16C. The thin film transistor 471is also a channel protection type thin film transistor. A sourceelectrode layer or a drain electrode layer 477 that is electricallyconnected to a semiconductor layer of the thin film transistor 471 iselectrically connected to a first electrode layer 472. The firstelectrode layer 472, an electroluminescent layer 473, and a secondelectrode layer 474 are sequentially stacked. At this time, if the firstelectrode layer 472 and the second electrode layer 474 are both formedusing a material having light-transmitting property at least in avisible region or are both formed to have thicknesses that can transmitlight, dual emission is realized. In this case, an insulating layer andthe substrate 470 through which light is transmitted are also requiredto have light-transmitting property to light in a visible region.

Modes of a light-emitting element which is applicable in this embodimentmode are shown in FIGS. 15A to 15D. FIGS. 15A to 15D show elementstructures of the light-emitting element, and the light-emitting elementhas a structure in which an electroluminescent layer 860 formed of anorganic compound and an inorganic compound is interposed between a firstelectrode layer 870 and a second electrode layer 850. Theelectroluminescent layer 860 is, as shown in the figure, structured by afirst layer 804, a second layer 803, and a third layer 803.

First, the first layer 804 is a layer which has a function oftransporting holes to the second layer 803, and includes at least afirst organic compound and a first inorganic compound havingelectron-accepting property with respect to the first organic compound.What is important is that the first organic compound and the firstinorganic compound are not simply mixed but the first inorganic compoundhas the electron-accepting property with respect to the first organiccompound. This structure generates many hole-carriers in the firstorganic compound which has originally almost no inherent carriers, andhole-injecting and hole-transporting property which are highly excellentcan be exhibited.

Therefore, the first layer 804 can obtain not only an advantageouseffect (e.g., improvement in heat resistance) that is considered to beobtained by mixing an inorganic compound but also excellent conductivity(in particular, hole-injecting property and hole-transporting propertyin the first layer 804). This is advantageous effect that cannot beobtained in a conventional hole-transporting layer in which an organiccompound and an inorganic compound that do not electronically interactwith each other are simply mixed. This advantageous effect can make adriving voltage lower than conventional one. In addition, since thefirst layer 804 can be made thick without causing increase in drivingvoltage, short circuit of the element due to dust or the like can besuppressed.

Since hole-carriers are generated in the first organic compound asdescribed above, it is preferable to use a hole-transporting organiccompound as the first organic compound. Examples of thehole-transporting organic compound include, but are not limited to,phthalocyanine (abbreviation: H₂Pc), copper phthalocyanine(abbreviation: CuPc), vanadyl phthalocyanine (abbreviation: VOPc),4,4′,4″-tris(N,N-diphenylamino)triphenylamine (abbreviation: TDATA),4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine(abbreviation: MTDATA), 1,3,5-tris[N,N-di(m-tolyl)amino]benzene(abbreviation: m-MTDAB),N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine(abbreviation: TPD), 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl(abbreviation: NPB),4,4′-bis{N-[4-di(m-tolyl)amino]phenyl-N-phenylamino}biphenyl(abbreviation: DNTPD), 4,4′,4″-tris(N-carbazolyl)triphenylamine(abbreviation: TCTA), and the like. Among the compounds described above,an aromatic amine compound typified by TDATA, MTDATA, m-MTDAB, TPD, NPB,DNTPD, and TCTA can easily generate hole-carriers, and a suitablecompound group for the first organic compound.

On the other hand, the first inorganic compound may be any material aslong as the material can easily accept electrons from the first organiccompound, and various kinds of metal oxides and metal nitrides can beused. Any of transition metal oxides that belong to Groups 4 to 12 ofthe periodic table is preferable because electron-accepting property iseasily exhibited. Specifically, for example, titanium oxide, zirconiumoxide, vanadium oxide, molybdenum oxide, tungsten oxide, rhenium oxide,ruthenium oxide, zinc oxide, and the like can be given. In addition,among the metal oxides described above, any of transition metal oxidesthat belong to Groups 4 to 8 of the periodic table mostly has a highelectron-accepting property, which is a preferable group. In particular,vanadium oxide, molybdenum oxide, tungsten oxide, and rhenium oxide arepreferable because they can be formed by vacuum evaporation and can beeasily used.

Note that the first layer 804 may be formed by stacking a plurality oflayers each including a combination of the organic compound and theinorganic compound described above, and may further include anotherorganic compound or inorganic compound.

Next, the third layer 802 will be described. The third layer 802 is alayer which has a function of transporting electrons to the second layer803, and includes at least a third organic compound and a thirdinorganic compound having electron-donating property with respect to thethird organic compound. What is important is that the third organiccompound and the third inorganic compound are not simply mixed but thethird inorganic compound has the electron-denoting property with respectto the third organic compound. This structure generates manyelectron-carriers in the third organic compound which has originallyalmost no inherent carriers, and electron-injecting andelectron-transporting property which are highly excellent can beexhibited.

Therefore, the third layer 802 can obtain not only an advantageouseffect (e.g., improvement in heat resistance) that is considered to beobtained by mixing an inorganic compound but also excellent conductivity(in particular, electron-injecting property and electron-transportingproperty in the third layer 802). This is advantageous effect thatcannot be obtained in a conventional electron-transporting layer inwhich an organic compound and an inorganic compound that do notelectronically interact with each other are simply mixed. Thisadvantageous effect can make a driving voltage lower than conventionalone. In addition, since the third layer 802 can be made thick withoutcausing increase in driving voltage, short circuit of the element due todust or the like can be suppressed.

As the third organic compound in which electron-carriers are generatedas described above, it is preferable to use an electron-transportingorganic compound. Examples of the electron-transporting organic compoundinclude, but are not limited to, tris(8-quinolinolato)aluminum(abbreviation: Alq₃), tris(4-methyl-8-quinolinolato)aluminum(abbreviation: Almq₃), bis(10-hydroxybenzo[h]-quinolinato)beryllium(abbreviation: BeBq₂),bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum (abbreviation:BAlq), bis[2-(2′-hydroxyphenyl)benzoxazolato]zinc (abbreviation:Zn(BOX)₂), bis[2-(2′-hydroxyphenyl)benzothiazolato]zinc (abbreviation:Zn(BTZ)₂), bathophenanthroline (abbreviation: BPhen), bathocuproin(abbreviation: BCP),2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation:PBD), 1,3-bis[5-(4-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviation: OXD-7),2,2′,2″-(1,3,5-benzenetriyl)-tris(1-phenyl-1H-benzimidazole)(abbreviation: TPBI),3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole(abbreviation: TAZ),3-(4-biphenylyl)-4-(4-ethylphenyl)-5-(4-tert-butylphenyl)-1,2,4-triazole(abbreviation: p-EtTAZ), and the like. In addition, among the compoundsdescribed above, chelatemetal complexes having a chelate ligandincluding an aromatic ring typified by Alq₃, Almq₃, BeBq₂, BAlq,Zn(BOX)₂, and Zn(BTZ)₂, organic compounds having a phenanthrolineskeleton typified by BPhen and BCP, and organic compounds having anoxadiazole skeleton typified by PBD and OXD-7 can easily generateelectron-carriers, and are suitable compound groups for the thirdorganic compound.

On the other hand, the third inorganic compound may be any material aslong as the material can easily donate electrons to the third organiccompound, and various kinds of a metal oxide or a metal nitride can beused. An alkali metal oxide, an alkaline-earth metal oxide, a rare-earthmetal oxide, an alkali metal nitride, an alkaline-earth metal nitride,and a rare-earth metal nitride are preferable because electron-donatingproperty is easily exhibited. Specifically, for example, lithium oxide,strontium oxide, barium oxide, erbium oxide, lithium nitride, magnesiumnitride, calcium nitride, yttrium nitride, lanthanum nitride, and thelike can be given. In particular, lithium oxide, barium oxide, lithiumnitride, magnesium nitride, and calcium nitride are preferable becausethey can be formed by vacuum evaporation and can be easily used.

Note that the third layer 802 may be formed by stacking a plurality oflayers each including a combination of the organic compound and theinorganic compound described above, and may further include anotherorganic compound or inorganic compound.

Then, the second layer 803 will be described. The second layer 803 is alayer which has a function of emitting light, and includes a secondorganic compound that has light-emitting property. The second layer 803may also include a second inorganic compound. The second layer 803 canbe formed by using various light-emitting organic compounds or inorganiccompounds. However, since it is considered to be hard to flow a currentthrough the second layer 803 as compared with the first layer 804 or thethird layer 802, the thickness of the second layer 803 is preferablyapproximately 10 to 100 nm.

The second organic compound is not particularly limited as long as it isa light-emitting organic compound, and examples of the second organiccompound include 9,10-di(2-naphthyl)anthracene (abbreviation: DNA),9,10-di(2-naphthyl)-2-tert-butylanthracene (abbreviation: t-BuDNA),4,4′-bis(2,2-diphenylvinyl)biphenyl (abbreviation: DPVBi), coumarin 30,coumarin 6, coumarin 545, coumarin 545T, perylene, rubrene,periflanthene, 2,5,8,11-tetra(tert-butyl)perylene (abbreviation: TBP),9,10-diphenylanthracene (abbreviation: DPA), 5,12-diphenyltetracene,4-(dicyanomethylene)-2-methyl-[p-(dimethylamino)styryl]-4H-pyran(abbreviation: DCM1),4-(dicyanomethylene)-2-methyl-6-[2-(julolidine-9-yl)ethenyl]-4H-pyran(abbreviation: DCM2),4-(dicyanomethylene)-2,6-bis[p-(dimethylamino)styryl]-4H-pyran(abbreviation: BisDCM), and the like. In addition, a compound capable ofemitting phosphorescence can also be used, such asbis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(picolinate)(abbreviation: FIrpic),bis{2-[3′,5′-bis(trifluoromethyl)phenyl]pyridinato-N,C^(2′)}iridium(picolinate)(abbreviation: Ir(CF₃ ppy)₂(pic)),tris(2-phenylpyridinato-N,C^(2′))iridium (abbreviation: Ir(Ppy)₃),bis(2-phenylpyridinato-N,C^(2′))iridium(acetylacetonate) (abbreviation:Ir(ppy)₂(acac)),bis[2-(2′-thienyl)pyridinato-N,C^(3′)]iridium(acetylacetonate)(abbreviation: Ir(thp)₂(acac)),bis(2-phenylquinolinato-N,C^(2′))iridium(acetylacetonate) (abbreviation:Ir(pq)₂(acac)), orbis[2-(2′-benzothienyl)pyridinato-N,C^(3′)]iridium(acetylacetonate)(abbreviation: Ir(btp)₂(acac)).

Further, a triplet excitation light-emitting material containing a metalcomplex or the like may be used for the second layer 803, as well as asinglet excitation light-emitting material. For example, among pixelsemitting red, green, and blue light, a pixel emitting red light whoseluminance is reduced by half in a relatively short time is formed byusing a triplet excitation light-emitting material and the other pixelsare formed by using a singlet excitation light-emitting material. Atriplet excitation light-emitting material has a feature of highlight-emitting efficiency and less power consumption to obtain the sameluminance. That is, when a triplet excitation light-emitting material isused for a red pixel, the amount of current needs to be supplied to alight-emitting element is small; thus, reliability can be improved. Apixel emitting red light and a pixel emitting green light may be formedby using a triplet excitation light-emitting material and a pixelemitting blue light may be formed by using a singlet excitationlight-emitting material to achieve low power consumption as well. Lowpower consumption can be further achieved by forming a light-emittingelement emitting green light that has high visibility for human eyes, byusing a triplet excitation light-emitting material.

The second layer 803 may include not only the second organic compounddescribed above, which exhibits light emission, but also another organiccompound. Examples of organic compounds that can be added include, butare not limited to, TDATA, MTDATA, m-MTDAB, TPD, NPB, DNTPD, TCTA, Alq₃,Almq₃, BeBq₂, BAlq, Zn(BOX)₂, Zn(BTZ)₂, BPhen, BCP, PBD, OXD-7, TPBI,TAZ, p-EtTAZ, DNA, t-BuDNA, and DPVBi, which are mentioned above, and4,4′-bis(N-carbazolyl)biphenyl (abbreviation: CBP),1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (abbreviation: TCPB), and thelike. It is preferable that the organic compound, which is added inaddition to the second organic compound, has larger excitation energythan that of the second organic compound and be added by the largeramount than the second organic compound in order to make the secondorganic compound emit light efficiently (which makes it possible toprevent concentration quenching of the second organic compound).Alternatively, as another function, the added organic compound may emitlight along with the second organic compound (which makes it possible toemit white light or the like).

The second layer 803 may have a structure to perform color display byproviding a light-emitting layer having a different emission wavelengthrange for each pixel. Typically, light-emitting layers corresponding torespective colors of R (red), G (green), and B (blue) are formed. Alsoin this case, color purity can be improved and a pixel portion can beprevented from having a mirror surface (reflection) by providing afilter which transmits light of an emission wavelength range of thelight on the light-emission side of the pixel. By providing the filter,a circularly polarizing plate or the like that has been conventionallyrequired can be omitted, and further, loss of light emitted from thelight-emitting layer can be eliminated. Further, change in color tone,which occurs when the pixel portion (display screen) is obliquely seen,can be reduced.

Either a low molecular weight organic light-emitting material or a highmolecular weight organic light-emitting material may be used as amaterial of the second layer 803. A high molecular weight organiclight-emitting material is physically stronger as compared with a lowmolecular weight material and is superior in durability of the element.In addition, a high molecular weight organic light-emitting material canbe formed by coating; therefore, the element can be relatively easilymanufactured.

The emission color is determined depending on a material forming thelight-emitting layer; therefore, a light-emitting element which exhibitsdesired light-emission can be formed by selecting an appropriatematerial for the light-emitting layer. As a high molecular weightelectroluminescent material which can be used for forming alight-emitting layer, a polyparaphenylene-vinylene-based material, apolyparaphenylene-based material, a polythiophene-based material, or apolyfluorene-based material can be used.

As the polyparaphenylene-vinylene-based material, a derivative ofpoly(paraphenylenevinylene) [PPV] such aspoly(2,5-dialkoxy-1,4-phenylenevinylene) [RO-PPV],poly(2-(2′-ethyl-hexoxy)-5-methoxy-1,4-phenylenevinylene) [MEH-PPV], orpoly(2-(dialkoxyphenyl)-1,4-phenylenevinylene) [ROPh-PPV] can be used.As the polyparaphenylene-based material, a derivative ofpolyparaphenylene [PPP] such as poly(2,5-dialkoxy-1,4-phenylene)[RO-PPP] or poly(2,5-dihexoxy-1,4-phenylene) can be used. As thepolythiophene-based material, a derivative of polythiophene [PT] such aspoly(3-alkylthiophene) [PAT], poly(3-hexylthiophen) [PHT],poly(3-cyclohexylthiophen) [PCHT], poly(3-cyclohexyl-4-methylthiophene)[PCHMT], poly(3,4-dicyclohexylthiophene) [PDCHT],poly[3-(4-octylphenyl)-thiophene] [POPT], orpoly[3-(4-octylphenyl)-2,2bithiophene] [PTOPT] can be used. As thepolyfluorene-based material, a derivative of polyfluorene [PF] such aspoly(9,9-dialkylfluorene) [PDAF] or poly(9,9-dioctylfluorene) [PDOF] canbe used.

The second inorganic compound may be any inorganic compound as long aslight-emission of the second organic compound is not easily quenched bythe inorganic compound, and various kinds of metal oxides and metalnitrides can be used. In particular, a metal oxide that belongs to Group13 or 14 of the periodic table is preferable because light-emission ofthe second organic compound is not easily quenched, and specifically,aluminum oxide, gallium oxide, silicon oxide, and germanium oxide arepreferable. However, the second inorganic compound is not limitedthereto.

Note that the second layer 803 may be formed by stacking a plurality oflayers each including a combination of the organic compound and theinorganic compound described above, and may further include anotherorganic compound or inorganic compound. A layer structure of thelight-emitting layer can be changed, and modification as follows can bepermitted unless it departs from the scope and spirit of the presentinvention; an electrode layer dedicated for injecting electrons may beprovided or a light-emitting material may be dispersed, instead ofproviding a specific electron-injecting region or light-emitting region.

A light-emitting element formed by using the above materials emits lightby being forwardly biased. Pixels of a display device which is formedusing a light-emitting element can be driven by a simple matrix methodor an active matrix method. In any case, each pixel is emitted light byapplying a forward bias thereto at a specific timing; however, the pixelis in a non-light emitting state for a certain period. Reliability ofthe light-emitting element can be improved by applying a reverse biasduring the non-light emitting period. In a light-emitting element, thereis a deterioration mode in which emission intensity is decreased under aconstant driving condition or a deterioration mode in which a non-lightemitting region is enlarged in the pixel and luminance is apparentlydecreased. However, progression of deterioration can be slowed down byalternating current driving where bias is applied forwardly andreversely; thus, reliability of a light-emitting display device can beimproved. Additionally, either digital driving or analog driving can beapplied.

A color filter (colored layer) may be formed over the sealing substrate.The color filter (colored layer) can be formed by a evaporation methodor a droplet discharge method. High-definition display can be performedby the color filter (colored layer). This is because a broad peak can becompensated to be sharp in an emission spectrum each of R, G and B bythe color filter (colored layer). Further, the present invention is notlimited to full-color display using three kinds of pixels which are R,G, and B, full-color display using four kinds of pixels which are R, G,B, and W (white) may also be performed by converting the three-colorvideo data into four-color video data. By using four kinds of pixels,luminance is increased and dynamic image display can be performed.

Full-color display can be performed by forming a material emitting lightof a single color and combining with a color filter or a colorconversion layer. Preferably, the color filter (colored layer) or thecolor conversion layer is formed over, for example, a second substrate(sealing substrate) and attached to a substrate.

Needless to say, display of single-color emission may also be performed.For example, an area color type display device may be formed usingsingle-color emission. The area color type is suitable for a passivematrix display portion, and can mainly display letters and symbols.

Materials of the first electrode layer 870 and the second electrodelayer 850 are required to be selected considering the work function. Thefirst electrode layer 870 and the second electrode layer 850 can beeither an anode or a cathode depending on the pixel structure. In thecase where polarity of a driving thin film transistor is a p-channeltype, the first electrode layer 870 preferably serves as an anode andthe second electrode layer 850 preferably serves as a cathode as shownin FIG. 15A. In the case where polarity of the driving thin filmtransistor is an n-channel type, the first electrode layer 870preferably serves as a cathode and the second electrode layer 850preferably serves as an anode as shown in FIG. 15B. Materials that canbe used for the first electrode layer 870 and the second electrode layer850 will be described. It is preferable to use a material having a highwork function (specifically, a material having a work function of 4.5 eVor more) for each of the first electrode layer 870 and the secondelectrode layer 850, which serves as an anode, and a material having alow work function (specifically, a material having a work function of3.5 eV or less) for each of the first electrode layer 870 and the secondelectrode layer 850, which serves as a cathode. However, since the firstlayer 804 is superior in hole-injecting property and hole-transportingproperty and the third layer 802 is superior in electron-injectingproperty and electron-transporting property, both of the first electrodelayer 870 and the second electrode layer 850 are scarcely restricted bya work function, and various materials can be used for them.

Each light-emitting element shown in FIGS. 15A and 15B has a structurewhere light is extracted from the first electrode layer 870; thus, thesecond electrode layer 850 is not necessarily required to havelight-transmitting property. The second electrode layer 850 may bepreferably a film mainly containing an element of Ti, TiN,TiSi_(x)N_(y), Ni, W, WASi_(x), WN_(x), WASi_(x)N_(y), NbN, Cr, Pt, Zn,Sn, In, Ta, Al, Cu, Au, Ag, Mg, Ca, Li and Mo, or an alloy material or acompound material containing the element as its main component; or amulti-layer film thereof in a total thickness of 100 to 800 nm.

The second electrode layer 850 can be formed by a evaporation method, asputtering method, a CVD method, a printing method, a droplet dischargemethod, or the like.

Further, when the second electrode layer 850 is formed of alight-transmitting conductive material similarly to the material usedfor the first electrode layer 870, light is also extracted from thesecond electrode layer 850, thereby a dual emission structure can beobtained in which light emitted from the light-emitting element isemitted from both the first electrode layer 870 and the second electrodelayer 850.

Note that the light-emitting element of the present invention hasvariations by changing the kind of each of the first electrode layer 870or the second electrode layer 850.

FIG. 15B shows the case where the third layer 802, the second layer 803,and the first layer 804 are stacked in this order on the first electrodelayer 870 side, in the electroluminescent layer 860.

As described above, in the light-emitting element of the presentinvention, the layer interposed between the first electrode layer 870and the second electrode layer 850 is formed of the electroluminescentlayer 860 including a layer in which an organic compound and aninorganic compound are combined. The light-emitting element is anorganic-inorganic composite light-emitting element provided with layers(that is, the first layer 804 and the third layer 802) that providefunctions of high carrier-injecting property and highcarrier-transporting property by mixing an organic compound and aninorganic compound, where the functions are not obtainable from onlyeither one of the organic compound or the inorganic compound. Inaddition, although it is effective that each of the first layer 804 andthe third layer 802 is a layer in which an organic compound and aninorganic compound are combined, each layer may contain only one of anorganic compound and an inorganic compound as well.

Further, various methods can be used as a method for forming theelectroluminescent layer 860 which is a layer in which an organiccompound and an inorganic compound are mixed. A co-evaporation method bywhich both an organic compound and an inorganic compound are evaporatedat the same time can be employed. For example, there is a co-evaporationmethod of evaporating both an organic compound and an inorganic compoundby resistance heating. Besides, for co-evaporation, an inorganiccompound may be evaporated by an electron beam (EB) while evaporating anorganic compound by resistance heating. Moreover, there is a method ofsputtering an inorganic compound while evaporating an organic compoundby resistance heating to deposit the both at the same time. In addition,the electroluminescent layer may also be formed by a wet process.

Similarly, for forming the first electrode layer 870 and the secondelectrode layer 850, a evaporation method by resistance heating, an EBevaporation method, a sputtering method, a wet process, or the like canbe employed.

In FIG. 15C, an electrode layer having reflectivity is used as the firstelectrode layer 870 and an electrode layer having light-transmittingproperty is used as the second electrode layer 850 in FIG. 15A, so thatlight emitted from the light-emitting element is reflected on the firstelectrode layer 870, and transmitted and emitted through the secondelectrode layer 850. Similarly, in FIG. 15D, an electrode layer havingreflectivity is used as the first electrode layer 870 and an electrodelayer having light-transmitting property is used as the second electrodelayer 850 in FIG. 15B, so that light emitted from the light-emittingelement is reflected on the first electrode layer 870, and transmittedand emitted through the second electrode layer 850. This embodiment modecan be combined freely with each of Embodiment Modes 1 to 18.

Embodiment Mode 20

Next, a mode in which a driver circuit is mounted on a display device ofthe present invention will be described.

First, a display device using COG will be described using FIG. 18A. Thepixel portion 2701 which displays information such as letters and imagesis provided over the substrate 2700. A substrate provided with aplurality of driver circuits is cut into rectangular shape, and the cutdriver circuits (also referred to as driver ICs) 2751 are mounted on thesubstrate 2700. FIG. 18A shows a mode in which a plurality of the driverICs 2751, and the FPC 2750 which is attached to the end of each driverIC 2751 are mounted. Alternatively, the cut may be performed to have asize approximately equal to the side length on the signal line side ofthe pixel portion, and a single driver IC and a tape which is attachedto the end thereof may be mounted.

Further, TAB may also be adopted, and in this case, a plurality of tapesis pasted as shown in FIG. 18B, and each driver IC may be attached tothe tape. Similarly to the case of COG, a single driver IC may bemounted on a single tape; in this case, a metal piece or the like forfixing the driver IC may be attached together for intensity.

Such a driver IC to be mounted on the display panel is preferably formedover a rectangular substrate having a side of 300 mm to 1000 mm or more,in plural number in order to improve productivity.

That is, a plurality of circuit patterns each including a driver circuitportion and an input/output terminal as one unit may be formed over asubstrate, and be divided and taken out finally. As for the length of along side of the driver IC, a rectangle with a long side of 15 to 80 mmand a short side of 1 to 6 mm may be formed in consideration of a lengthof one side of a pixel portion or a pixel pitch, or one side of thepixel portion, or a length of one side of the pixel portion plus oneside of each driver circuit may be employed.

The advantage in outside dimension of the driver IC over an IC chip isthe length of the longer side. When a driver IC having a longer side of15 to 80 mm is used, the number of driver ICs necessary for mountingcorresponding to the pixel portion is smaller than that of IC chips;therefore, manufacturing yield can be enhanced. Further, when the driverIC is formed over a glass substrate, productivity is not detracted sincethe driver IC is not limited to a shape of a substrate used as a motherbody. This is a great advantage, as compared with the case of taking outIC chips from a circular silicon wafer.

In the case where the scanning line side driver circuit 3702 is formedover the same substrate as shown in FIG. 17B, a driver IC provided witha signal line side driver circuit is mounted in a region outside thepixel portion 3701. Such a driver IC is a signal line side drivercircuit. In order to form a pixel region corresponding to RGBfull-color, 3072 signal lines in a XGA class and 4800 signal lines in aUXGA class are necessary. The signal lines provided in theabove-described number form a leading out line by being divided intoseveral blocks at an edge of the pixel portion 3701 and are gathered inaccordance with a pitch of an output terminal of the driver IC. Thedriver IC can be formed of a crystalline semiconductor which is formedover a substrate.

Further, the driver IC may also be mounted as both a scanning linedriver circuit and a signal line driver circuit, as shown in FIGS. 18Aand 18B. In this case, it is preferable to make specifications ofrespective driver ICs used on the scanning line side and the signal lineside different. For example, as for the transistor for forming thescanning line side driver IC, although the withstand voltage required isapproximately 30 V, the drive frequency is 100 kHz or less and a highspeed operation is comparatively not required. Therefore, it ispreferable to set a sufficiently long channel-length (L) of thetransistor for forming the scanning line side driver. On the other hand,as for the transistor for forming the signal line side driver IC,although a withstand voltage of approximately 12 V is enough, the drivefrequency is approximately 65 MHz at 3 V and a high speed operation isrequired. Therefore, it is preferable to set the channel-length or thelike of the transistor for forming a driver with a micron rule.

The driver IC is formed to have the same thickness as that of a countersubstrate. Accordingly, they can have almost the same height, whichcontributes to reduce the thickness of a display device as a whole. Inaddition, the substrates are formed of the same material; therebythermal stress is not generated even when the temperature in the displaydevice is changed, and thus properties of the circuit comprising TFTsare not damaged. Moreover, as described in this embodiment, a drivercircuit is mounted with a driver IC that is longer than an IC chip sothat the number of driver ICs to be mounted per pixel region can bereduced.

As described above, a driver circuit can be incorporated in a displaypanel.

Embodiment Mode 12

An example of a protection circuit provided for a display device of thepresent invention will be described.

As shown in FIGS. 18A and 18B, a protection circuit 2713 can be formedbetween an external circuit and an internal circuit. The protectioncircuit includes one or more elements selected from a TFT, a diode, aresistor, a capacitor, and the like. Several structures of theprotection circuit and operation thereof will be described below. First,configurations of an equivalent circuit diagram of a protection circuitcorresponding to one input terminal and is disposed between the externalcircuit and the internal circuit will be described using FIGS. 19A to19E. The protection circuit shown in FIG. 19A includes p-channel thinfilm transistors 7220 and 7230, capacitors 7210 and 7240, and a resistor7250. The resistor 7250 has two terminals; one of which is supplied withan input voltage Vin (hereinafter referred to as Vin), and the other ofwhich is supplied with a low-potential voltage VSS (hereinafter referredto as VSS).

FIG. 19B is an equivalent circuit diagram of a protection circuit inwhich the p-channel thin film transistors 7220 and 7230 are substitutedby rectifying diodes 7260 and 7270. FIG. 19C is an equivalent circuitdiagram of a protection circuit in which the p-channel thin filmtransistors 7220 and 7230 are substituted by TFTs 7350, 7360, 7370, and7380. In addition, as a protection circuit having a differentconfiguration from the above configurations, FIG. 19D shows a protectioncircuit which includes resistors 7280 and 7290 and an n-channel thinfilm transistor 7300. A protection circuit shown in FIG. 19E includesresistors 7280 and 7290, a p-channel thin film transistor 7310, and ann-channel thin film transistor 7320. By providing the protectioncircuit, sudden change in electric potential can be prevented, andelement breakdown or damage can be prevented, which improvesreliability. Note that each element for forming the above-describedprotection circuit is preferably formed of an amorphous semiconductorthat can withstand high voltage. This embodiment mode can be freelycombined with the aforementioned embodiment modes.

Embodiment Mode 13

A television device can be completed by using a display device formed inaccordance with the present invention. FIG. 20 is a block diagramshowing a main structure of the television device. As for a displaypanel, any mode of the following may be employed: in the structure shownin FIG. 17A, a case where only a pixel portion 601 is formed and ascanning line side driver circuit 603 and a signal line side drivercircuit 602 are mounted by TAB as shown in FIG. 18B; in the structureshown in FIG. 17A, a case where only the pixel portion 601 is formed andthe scanning line side driver circuit 603 and the signal line sidedriver circuit 602 are mounted by COG as shown in FIG. 18A; a case wherea TFT is formed as shown in FIG. 17B, the pixel portion 601 and thescanning line side driver circuit 603 are formed over the samesubstrate, and the signal line side driver circuit 602 is independentlymounted as a driver IC; and a case where the pixel portion 601, thesignal line side driver circuit 602, and the scanning line side drivercircuit 603 are formed over the same substrate as shown in FIG. 17C; andthe like.

In addition, as another structure of an external circuit, a video signalamplifier circuit 605 which amplifies a video signal among signalsreceived by a tuner 604, a video signal processing circuit 606 whichconverts the signals output from the video signal amplifier circuit 605into chrominance signals corresponding to respective colors of red,green, and blue, a control circuit 607 which converts the video signalinto an input specification of a driver IC, or the like are provided onan input side of the video signal. The control circuit 607 outputssignals to both a scanning line side and a signal line side. In the caseof digital driving, a signal dividing circuit 608 may be provided on thesignal line side and an input digital signal may be divided into mpieces to be supplied.

An audio signal among signals received by the tuner 604 is sent to anaudio signal amplifier circuit 609 and is supplied to a speaker 613through an audio signal processing circuit 610. A control circuit 611receives control information of a receiving station (receptionfrequency) or sound volume from an input portion 612 and transmitssignals to the tuner 604 or the audio signal processing circuit 610.

A television device can be completed by incorporating such a displaymodule into a chassis as shown in FIG. 21A or 21B. A display panel asshown in FIGS. 1A and 1B also provided with an FPC is generally alsocalled an EL display module. Therefore, when the EL display module asshown in FIGS. 1A and 1B is used, an EL television device can becompleted. A main screen 2003 is formed using the display module, and aspeaker portion 2009, an operation switch, and the like are provided asits accessory equipment. Thus, a television device can be completed inaccordance with the present invention.

Further, reflected light of light entering from outside may be shieldedusing a phase difference plate or a polarizing plate. In the case of atop emission display device, an insulating layer to be a partition wallmay be colored and used as a black matrix. The partition wall can alsobe formed by a droplet discharge method or the like. Carbon black or thelike may be mixed into a black resin of a pigment material or a resinmaterial such as polyimide, and a stack-layer structure thereof may alsobe used. By a droplet discharge method, different materials may bedischarged to the same region plural times to form the partition wall. Aquarter wave plate and a half wave plate may be used as the phasedifference plates so that design may be performed so as to controllight. As the structure, the light-emitting element, the sealingsubstrate (sealant), the phase difference plates (a quarter wave plateand a half wave plate), and the polarizing plate are sequentiallystacked over a TFT element substrate, in which light emitted from thelight-emitting element is transmitted therethrough and emitted outsidefrom a polarizing plate side. The phase difference plates and thepolarizing plate may be provided on a side where light is emittedoutside or may be provided on both sides in the case of a dual emissiondisplay device in which light is emitted from both the surfaces. Inaddition, an anti-reflective film may be provided on the outer side ofthe polarizing plate. Accordingly, a higher-definition and more accurateimage can be displayed.

As shown in FIG. 21A, a display panel 2002 utilizing a display elementis incorporated in a chassis 2001, and general TV broadcast can bereceived by a receiver 2005. In addition, by connecting to acommunication network by wired or wireless connections via a modem 2004with the receiver 2005, one-way (from a sender to a receiver) or two-way(between a sender and a receiver or between receivers) informationcommunication can be carried out. The television device can be operatedby using a switch built in the chassis or a remote control unit 2006. Adisplay portion 2007 for displaying output information may also beprovided in the remote control unit 2006.

Further, the television device may include a sub screen 2008 formedusing a second display panel to display channels, volume, or the like,in addition to the main screen 2003. In this structure, the main screen2003 may be formed using an EL display panel having wide viewing angle,and the sub screen 2008 may be formed using a liquid crystal displaypanel capable of displaying images with lower power consumption. Inorder to reduce the power consumption preferentially, the main screen2003 may be formed using a liquid crystal display panel, and the subscreen 2008 may be formed using an EL display panel such that the subscreen can flash on and off. Needless to say, both of the main screenand the sub screen can be formed using an EL display panel to which thepresent invention is applied. By using the present invention, a highlyreliable display device can be formed.

FIG. 20B shows a television device having a large display portion with asize of, for example, 20 to 80 inches. The television device includes achassis 2010, a display portion 2011, a remote control unit 2012 that isan operation portion, a speaker portion 2013, and the like. The presentinvention is applied to manufacturing of the display portion 2011. Thetelevision device shown in FIG. 21B which is a wall-hanging type doesnot require a large installation space.

Needless to say, the present invention can be applied not only to atelevision device, but also to various use applications; e.g., alarge-sized display medium such as an information display board at arailway station, an airport, or the like, or an advertisement displayboard on a street, as well as a monitor of a personal computer.

The television device to which the present invention is applied has highperformance and high reliability. In addition, it can be manufactured ata low cost; therefore, since purchase at low price is possible, thetelevision device of the present invention is suitable for the case ofbeing used outdoors or the like where wear or deterioration proceedsfast and frequent replacement is required, such as for a informationdisplay panel at a railway station, an airport, or the like or anadvertisement display panel on a street.

By using the present invention, since the number of wires can be reducedin each pixel, the aperture ratio can be improved and the manufacturingprocess can be simplified. Consequently, such a highly reliable displaydevice can be manufactured with a high yield.

Embodiment Mode 23

By applying the present invention, various kinds of display devices canbe manufactured. That is, the present invention can be applied tovarious kinds of electronic devices incorporating such a display devicein the display portion.

As examples of the electronic devices, a camera such as a video cameraor a digital camera; a projector; a head-mounted display (a goggle typedisplay); a car navigation system; a car stereo; a personal computer; agame machine; a portable information terminal (e.g., a mobile computer,a cellular phone, or an electronic book); an image reproducing deviceprovided with a recording medium (specifically, a device which canreproduce a recording medium such as a digital versatile disk (DVD) andincludes a display capable of displaying images thereof); and the likecan be given. Specific examples thereof are shown in FIGS. 24A to 24E.

The present invention can be used in a display portion of the electronicdevices shown in FIGS. 24A to 24E. Using the display device described inEmbodiment Modes 1 to 21, the display portion can be formed. Asdescribed in the aforementioned embodiment modes, the display portioncan be formed at a low cost with a high yield by applying the presentinvention. Further, high performance and high reliability can also beprovided for an electronic device manufactured.

FIG. 24A shows a personal computer, which includes a main body 2101, achassis 2102, a display portion 2103, a keyboard 2104, an externalconnection port 2105, a pointing mouse 2106, or the like. The displayportion 2103 can be manufactured using the present invention, to providehigh performance and high reliability. Further, the aperture ratio canbe high in the display portion, so that clear and bright images can bedisplayed even in the case of a display portion of a small electronicdevice.

FIG. 24B shows an image reproducing device (specifically, a DVDreproducing device) including a recording medium, which includes a mainbody 2201, a chassis 2202, a display portion A 2203, a display portion B2204, a recording medium (e.g., a DVD) reading portion 2205, anoperation key 2206, a speaker portion 2207, or the like. The displayportion A 2203 mainly displays video information, while the displayportion B 2204 mainly displays character information. These displayportion A 2203 and display portion B 2204 can be manufactured using thepresent invention, to provide high performance and high reliability.Further, the aperture ratio can be high in the display portion, so thatclear and bright images can be displayed even in the case of a displayportion of a small electronic device.

FIG. 24C shows a cellular phone, which includes a main body 2301, anaudio output portion 2302, an audio input portion 2303, a displayportion 2304, operation switches 2305, an antenna 2306, or the like. Byapplying the display device manufactured using the present invention tothe display portion 2304, high performance and high reliability can beprovided. Further, the aperture ratio can be high in the displayportion, so that clear and bright images can be displayed even in thecase of a display portion of a small electronic device.

FIG. 24D shows a video camera, which includes a main body 2401, adisplay portion 2402, a chassis 2403, an external connection port 2404,a remote control receiver 2405, an image receiving portion 2406, abattery 2407, an audio input portion 2408, operation keys 2409, or thelike. The present invention can be applied to the display portion 2402.By applying the display device manufactured using the present inventionto the display portion 2402, high performance and high reliability canbe provided. Further, the aperture ratio can be high in the displayportion, so that clear and bright images can be displayed even in thecase of a display portion of a small electronic device.

FIG. 24E shows a digital player, which includes a main body 2501, adisplay portion 2502, operation keys 2503, a recording medium 2504, anearphone 2506 which is a small device for converting an electricalsignal into an audio signal, or the like. The digital player shown inFIG. 24E records and plays sounds (music) and images and a flash memoryis used for the recording medium 2504 which has capacitance of 20 to 200GB. The present invention can be applied to the display portion 2502. Byapplying the display device manufactured using the present invention tothe display portion 2502, high performance and high reliability can beprovided. Further, the aperture ratio can be high in the displayportion, so that clear and bright images can be displayed even in thecase of a display portion of a small electronic device.

Embodiment Mode 24

An example in which the display device described in the aforementionedembodiment modes is applied to a display device having flexibility willbe described with reference to FIG. 22, as this embodiment mode.

A display device of the present invention shown in FIG. 22 may beincluded in a housing, and includes a main body 660, a pixel portion 661which displays an image, a driver IC 662, a receiver device 663, a filmbattery 664, or the like. The driver IC, the receiver device, and thelike may be mounted using a semiconductor component. The main body 660of the display device of the present invention is formed using amaterial having flexibility such as plastic or a film.

The display device of the present invention can manufacture a displaydevice having a high aperture ratio and high reliability with a highyield.

Further, such a display device is extremely light and flexible;therefore, the display device which can be rolled into a cylinder shapeis extremely advantageous to carry around. By the display device of thepresent invention, a display medium with a large screen can be freelycarried around.

Moreover, the display device as shown in FIG. 22 can be used as a meansfor mainly displaying a still image for electrical home appliances suchas a refrigerator, a washing machine, a rice cooker, a fixed telephone,a vacuum cleaner, or a clinical thermometer, and a large-sizedinformation display such as strap advertisement in a train or an arrivaland departure guide plate at a railway station or an airport, as well asa navigation system, an audio reproducing device (e.g., a car audio oran audio component), a personal computer, a game machine, or a portableinformation terminal (e.g., a mobile computer, a cellular phone, aportable game machine, or an electronic book).

Although the preferred embodiment modes of the present invention arespecifically described as set forth above, it is to be understood thatvarious changes and modifications will be apparent to those skilled inthe art, unless such changes and modifications depart from the scope ofthe present invention.

This application is based on Japanese Patent Application serial no.2005345341 filed in Japan Patent Office on 30th, Nov. 2005, the entirecontents of which are hereby incorporated by reference.

1. A display device comprising: a light-emitting element; a firstswitch; a second switch; a transistor; a first capacitor; and a secondcapacitor, wherein one terminal of the first switch is electricallyconnected to a first electrode of the second capacitor, wherein a secondelectrode of the second capacitor is electrically connected to oneterminal of the second switch and a first electrode of the firstcapacitor, wherein a second electrode of the first capacitor iselectrically connected to a first wire, wherein a gate of the transistoris electrically connected to the first electrode of the secondcapacitor, one of a source and a drain of the transistor is electricallyconnected to a first electrode of the light-emitting element, and theother of the source and the drain of the transistor is electricallyconnected to the other terminal of the second switch, and wherein asecond electrode of the light-emitting element and the other terminal ofthe first switch are electrically connected to a same second wire. 2.The display device according to claim 1, wherein the first switch andthe second switch are transistors.
 3. The display device according toclaim 1, wherein the second wire is maintained at a fixed potential. 4.The display device according to claim 2, wherein the transistors arethin film transistors.
 5. The display device according to claim 1,wherein the other of the source and the drain of the transistor iselectrically connected to a third wire.
 6. A display device comprising:a light-emitting element; a first switch; a second switch; a thirdswitch; a fourth switch; a transistor; a first capacitor; and a secondcapacitor, wherein one terminal of the first switch is electricallyconnected to a first electrode of the second capacitor, and a secondelectrode of the second capacitor is electrically connected to oneterminal of the second switch and a first electrode of the firstcapacitor, wherein a second electrode of the first capacitor iselectrically connected to a first wire, wherein one terminal of thethird switch is electrically connected to the second electrode of thesecond capacitor, and the other terminal of the third switch iselectrically connected to a second wire, wherein a gate of thetransistor is electrically connected to the first electrode of thesecond capacitor, one of a source and a drain of the transistor iselectrically connected to a first electrode of the light-emittingelement, and the other of the source and the drain of the transistor iselectrically connected to the other terminal of the second switch andone terminal of the fourth switch, and wherein a second electrode of thelight-emitting element and the other terminal of the first switch areelectrically connected to a same third wire.
 7. The display deviceaccording to claim 6, wherein the first switch, the second switch, thethird switch, and the fourth switch are transistors.
 8. The displaydevice according to claim 6, wherein the third wire is maintained at afixed potential.
 9. The display device according to claim 7, wherein thetransistors are thin film transistors.
 10. The display device accordingto claim 6, wherein the other terminal of the fourth switch iselectrically connected to a fourth wire.
 11. A display devicecomprising: a light-emitting element; a first switch; a second switch; athird switch; a fourth switch; a fifth switch; a transistor; a firstcapacitor; and a second capacitor, wherein one terminal of the firstswitch is electrically connected to a first electrode of the secondcapacitor, and a second electrode of the second capacitor iselectrically connected to one terminal of the second switch and a firstelectrode of the first capacitor, wherein a second electrode of thefirst capacitor is electrically connected to a first wire, wherein oneterminal of the third switch is electrically connected to the secondelectrode of the second capacitor, and the other terminal of the thirdswitch is electrically connected to a second wire, wherein a gate of thetransistor is electrically connected to the first electrode of thesecond capacitor, one of a source and a drain of the transistor iselectrically connected to a first electrode of the light-emittingelement, and the other of the source and the drain of the transistor iselectrically connected to the other terminal of the second switch andone terminal of the fourth switch, wherein one terminal of the fifthswitch is electrically connected to the first electrode of thelight-emitting element, and wherein a second electrode of thelight-emitting element, the other terminal of the first switch and theother terminal of the fifth switch are electrically connected to a samethird wire.
 12. The display device according to claim 11, wherein thefirst switch, the second switch, the third switch, the fourth switch andthe fifth switch are transistors.
 13. The display device according toclaim 11, wherein the third wire is maintained at a fixed potential. 14.The display device according to claim 12, wherein the transistors arethin film transistors.
 15. The display device according to claim 11,wherein the other terminal of the fourth switch is electricallyconnected to a fourth wire.